Vertebral Column Anatomy PDF

Describe the norm aland abnorm alcurvatures ofthe vertebral Figure 2.1 colum n (prim ary,secondary,kyphosis,lordosis,and scoliosis) Vertebralcolum n and curvatures.A–C.Regions ofadultvertebralcolum n. Zygapop...

Describe the norm aland abnorm alcurvatures ofthe vertebral Figure 2.1 colum n (prim ary,secondary,kyphosis,lordosis,and scoliosis) Vertebralcolum n and curvatures.A–C.Regions ofadultvertebralcolum n. Zygapophysial(facet) joints representative of each region are circled.D. Curvatures ofadult vertebralcolum n.E. Curvatures offetal vertebralcolum n. The vertebral column protects the spinal cord and spinal nerves and supports the weight of the body. The adult vertebral column typically consists of 33 vertebrae arranged in five regions: 7 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 4 coccygeal (Fig. 2.1A–D). It has four curvatures: cervical, thoracic, lumbar, and sacral (Fig. 2.1D). The thoracic and sacral (pelvic) curvatures (kyphoses) are concave anteriorly, whereas the cervical and lumbar curvatures (lordoses) are concave posteriorly. The thoracic and sacral curvatures are primary curvatures developing during the fetal period (Fig. 2.1E). The cervical and lumbar curvatures are secondary curvatures, which begin to appear in the cervical region during the fetal period but do not become obvious until infancy. 2  Describe the norm aland abnorm alcurvatures ofthe vertebral Figure B2.1 colum n (prim ary,secondary,kyphosis,lordosis,and scoliosis) Norm aland abnorm al curvatures of vertebral colum n. Excessive lumbar lordosis (clinically shortened to lordosis) is characterized by an anterior rotation of the pelvis, producing an abnormal increase in the lumbar curvature and may be associated with weakened trunk musculature, especially of the anterolateral abdominal wall. To compensate for alterations to their normal line of gravity, women develop a temporary lordosis during late pregnancy. Excessive thoracic kyphosis (clinically shortened to kyphosis) is characterized by an abnormal increase in the thoracic curvature and can result from erosion of the anterior part of one or more vertebrae. Scoliosis (curved back) is characterized by an abnormal lateral curvature that is accompanied by rotation of the vertebrae (Fig. B2.1F, G) and is the most common deformity of the vertebral column in pubertal girls (aged 12 to 15 years). Asymmetric weakness of the intrinsic back muscles (myopathic scoliosis), failure of half of a vertebra to develop (hemivertebra), and a difference in the length of the lower limbs are causes of scoliosis. 3  Identify the parts oftypicaland atypicalvertebra (including on Figure 2.2 radiographs)and describe the features ofeach regionaltype Typicalvertebra, represented by second lum bar vertebra.A and B. Bony features.C. Functionalcom ponents.D. Form ation ofIV foram en. Vertebrae vary in size and other characteristics from one region of the vertebral column to another and within each region. The succession of vertebral foramina in the articulated column forms the vertebral canal, which contains the spinal cord, meninges (protective membranes), fat, spinal nerve roots, and vessels. The superior and inferior vertebral notches of adjacent vertebrae combine to form the intervertebral (IV) foramina, which give passage to spinal nerve roots and accompanying vessels and contain the spinal ganglia (Fig. 2.2D). Seven processes arise from the vertebral arch of a typical vertebra (Fig. 2.2): One median spinous process projects posteriorly from the vertebral arch at the junction of the laminae. Two transverse processes project posterolaterally from the junctions of the pedicles and laminae. Four articular processes—two superior and two inferior—also arise from the junctions of the pedicles and laminae, each bearing an articular surface (facet). The spinous process and two transverse processes project from the vertebral arch and provide attachments for deep back muscles, serving as levers in moving the vertebrae (Fig. 2.2C). The four articular processes are in apposition with corresponding processes of vertebrae superior and inferior to them, forming zygapophysial (facet) joints (Fig. 2.2D). 4  Identify the parts oftypicaland atypicalvertebra (including on Figure 2.3 radiographs)and describe the features ofeach regionaltype Cervicalvertebrae.A and B.Articulated vertebrae.C. Radiograph.D–F.Bony features oftypicalcervical vertebrae. 5  Identify the parts oftypicaland atypicalvertebra (including on Figure 2.4 radiographs)and describe the features ofeach regionaltype Atlas (C1) and axis (C2).A and B.Bony features.C and D.Radiograph with correlative illustration.E. Three-dim ensionalCT reconstruction ofcervical spine. 6  Identify the parts oftypicaland atypicalvertebra (including on Figure 2.5 radiographs)and describe the features ofeach regionaltype Thoracic vertebrae.Thoracic vertebrae (T1–T12)form the posterior part ofthe skeleton of the thorax and articulate w ith the ribs.A.Bony features of typicalvertebra.B.Radiograph showing articulations ofribs w ith vertebralcolum n.C.Bony features oftypicalvertebra.D. Articulated vertebrae.E. Radiograph ofthoracic spine. The apparentspace betw een the vertebralbodies in radiographs is the site ofthe radiolucentIV disc. 7  Identify the parts oftypicaland atypicalvertebra (including on Figure 2.6 radiographs)and describe the features ofeach regionaltype Lum bar vertebrae.A and B.Bony features.C–E. Radiographs oflum bar spine.Letters in partD refer to structures labeled in partC. The joints of the vertebral arches are the zygapophysial joints (facet joints), synovial, plane joints between the superior and the inferior articular processes of adjacent vertebrae. Each joint is surrounded by a thin, loose joint (articular) capsule, which is attached to the margins of the articular surfaces of the articular processes of adjacent vertebrae (Fig. 2.10C). The zygapophysial joints permit gliding movements between the articular processes; the shape and disposition of the articular surfaces determine the type of movement possible. 8  Identify the parts oftypicaland atypicalvertebra (including on Figure 2.7 radiographs)and describe the features ofeach regionaltype Sacrum and coccyx.A. Base and pelvic surface.B. Radiograph showing features ofsacrum.C. Posterior surface.D. Coronalsection through 1stsacralforam ina. The wedge‐shaped sacrum in adults is composed of five fused sacral vertebrae. The base of the sacrum is formed by the superior surface of the S1 vertebra. Its superior articular processes articulate with the inferior articular processes of the L5 vertebra. The projecting anterior edge of the body of the first sacral vertebra is the sacral promontory. On the pelvic and dorsal surfaces are four pairs of sacral foramina for the exit of the rami of the first four sacral nerves and the accompanying vessels. The fused spinous processes form the median sacral crest. The fused articular processes form the intermediate sacral crests, and the fused tips of the transverse processes form the lateral sacral crests. The inverted U‐shaped sacral hiatus leads into the sacral canal, the inferior end of the vertebral canal. The sacral cornua project inferiorly on each side of the sacral hiatus and are a helpful guide to its location. The lateral surface of the sacrum has an ear‐shaped (auricular) articular surface that participates in the sacro‐ iliac joint. The are four vertebrae of the coccyx which are typically fused. 9  Describe the organization (bones,joints,ligam ents), Figure 2.8 function and m ovem ents ofthe vertebralcolum n Structure and function of intervertebral(IV) discs. A.Ligam ents.B and C. Structure ofIV disc.D. Non–weight-bearing IV disc.E and F.IV disc during loading and m ovem ent. The joints of the vertebral bodies are symphyses (secondary cartilaginous joints) designed for weight bearing and strength. The articulating surfaces of adjacent vertebrae are connected by IV discs and ligaments (Fig. 2.8). As well as permitting movement between adjacent vertebrae, the discs have resilient deformability, which allows them to serve as shock absorbers. Each IV disc consists of an anulus fibrosus, an outer fibrous part, and a gelatinous central mass, the nucleus pulposus. There is no IV disc between the C1 (atlas) and C2 (axis) vertebrae and the most inferior disc is between the L5 and S1 vertebrae. 10  Describe the organization (bones,joints,ligam ents), Figure 2.9 function and m ovem ents ofthe vertebralcolum n Uncovertebraljoints. These joints are atthe posterolateralm argin of the cervicalIV discs. Uncovertebral “joints” (of Luschka) are located between the uncus of the bodies of the C3–C6 vertebrae and the inferolateral surfaces of the vertebral bodies superior to them (Fig. 2.9). The joints are at the lateral and posterolateral margins of the IV discs. The uncovertebral joints are frequent sites of spur formation (projecting processes of bone) that may cause neck pain. 11  Describe the organization (bones,joints,ligam ents), Figure 2.10 function and m ovem ents ofthe vertebralcolum n Joints and ligam ents of vertebral colum n.A.Relationship ofligam ents to vertebrae and IV discs.The pedicles of the superior vertebrae have been saw n through,and their bodies have been rem oved.A rib and its costovertebral joint and associated ligam ents are also show n.B.Transverse section ofan IV disc.The nucleus pulposus has been rem oved to show the hyaline cartilage plate covering the superior surface of the vertebralbody.C.Ligam ents of thoracic region.The vertebralarch of the superior vertebra has been rem oved to show the posterior longitudinalligam ent.D.Ligam ents of cervicalregion. The anterior longitudinal ligament is a strong, broad fibrous band that covers and connects the anterolateral aspects of the vertebral bodies and IV discs (Figs. 2.8A and 2.10A) and limits extension of the vertebral column. The posterior longitudinal ligament runs within the vertebral canal along the posterior aspect of the vertebral bodies (Fig. 2.10A, C) and helps prevent hyperflexion of the vertebral column and posterior herniation of the IV discs. The laminae of adjacent vertebral arches are joined by broad, pale, yellow elastic fibrous tissue called the ligamenta flava which resist separation of the vertebral laminae by arresting abrupt flexion of the vertebral column and thereby preventing injury to the IV discs. Adjacent spinous processes are united by weak interspinous ligaments and strong fibrous supraspinous ligaments (Fig. 2.10B, C). The supraspinous ligament merges superiorly with the nuchal ligament, the strong median ligament of the neck (Fig. 2.10D). 12  Describe the organization (bones,joints,ligam ents), Figure 2.12 function and m ovem ents ofthe vertebralcolum n Craniovertebraljoints.A. Ligam ents ofatlantooccipitaland atlantoaxialjoints.The large vertebralforam en ofthe atlas (C1 vertebra)is divided into two foram ina by the transverse ligam entofatlas.The larger posterior foram en is for the spinal cord,and the sm aller anterior foram en is for the dens ofthe axis (C2 vertebra).B.Hem isected craniovertebralregion.The m edian joints and m em branous continuities ofthe ligam enta flava and longitudinalligam ents in the craniovertebralregion are shown. C.Bands ofcruciate ligam ent. The craniovertebral joints include the atlantooccipital joints, between the atlas (C1 vertebra) and the occipital bone of the cranium, and the atlantoaxial joints, between the C1 and the C2 vertebrae (Fig. 2.12). These craniovertebral articulations are synovial joints that have no IV discs. The atlantooccipital joints, between the lateral masses of C1 (atlas) and the occipital condyles (Fig. 2.12C), permit nodding of the head, such as the neck flexion and extension that occurs when indicating approval (the “yes” movement). There are three atlantoaxial articulations: two (right and left) lateral atlantoaxial joints between the lateral masses of C1 and the superior facets of C2 (Fig. 2.12C) and one median atlantoaxial joint between the dens of C2 and the anterior arch and transverse ligament of the atlas (Fig. 2.12A, B). Movement at all three atlantoaxial joints permits the head to be turned from side to side, as occurs when rotating the head to indicate disapproval (the “no” movement). 13  Describe the m ajor features ofthe spinalcord,m eninges,and Figure 2.17 m eningealspaces and their relationships within the vertebralcanal Relationship of vertebral colum n,spinalcord,and spinalnerves.A. Schem atic.B.Cauda equina.Note the relation ofthe spinalcord segm ents and spinal nerves to the vertebral colum n. The spinal cord begins as a continuation of the medulla oblongata, the caudal part of the brainstem. In the newborn, the inferior end of the spinal cord usually is opposite the IV disc between the L2 and the L3 vertebrae. In adults, the spinal cord usually ends opposite the IV disc between the L1 and the L2 vertebrae. The spinal cord is enlarged in two regions for innervation of the limbs: The cervical enlargement extends from the C4 through the T1 segments of the spinal cord, and most of the anterior rami of the spinal nerves arising from it form the brachial plexus of nerves, which innervates the upper limbs. The lumbosacral (lumbar) enlargement extends from the L1 through the S3 segments of the spinal cord, and the anterior rami of the spinal nerves arising from it contribute to the lumbar and sacral plexuses of nerves, which innervate the lower limbs. The spinal nerve roots arising from the lumbosacral enlargement and conus medullaris (the tapered end of the spinal cord) form the cauda equina, the bundle of spinal nerve roots running inferior to the spinal cord through the lumbar cistern (subarachnoid space). 2  Describe the m ajor features ofthe spinalcord,m eninges,and Figure 2.17 m eningealspaces and their relationships within the vertebralcanal Continued. In adults, the spinal cord is shorter than the vertebral column; hence, there is a progressive obliquity of the spinal nerve roots as the cord descends (Fig. 2.17). The lumbar and sacral nerve rootlets descend until they reach the IV foramina of exit in the lumbar and sacral regions of the vertebral column, respectively. The bundle of spinal nerve roots in the lumbar cistern of the subarachnoid space caudal to the termination of the spinal cord resembles a horse’s tail, hence its name cauda equina (Fig. 2.17B). The inferior end of the spinal cord has a conical shape and tapers into the conus medullaris. From its inferior end, the filum terminale internum, which consists of primarily of pia mater, descends among the spinal nerve roots in the cauda equina. The filum terminale penetrates the inferior end of the dural sac becoming the filum terminale externum that passes through the sacral hiatus to attach ultimately to the coccyx posteriorly. The filum terminale serves as an anchor for the inferior ends of the spinal cord and dural sac. 3  Describe the m ajor features ofthe spinalcord,m eninges,and Figure 2.18 m eningealspaces and their relationships within the vertebralcanal Spinalcord and spinal m eninges.A.Cross section of spinalcord w ithin its m eninges. B.Duralsac cutopen.The m eninges have been cutand spread out.The pia m ater covers the spinalcord and projects laterally as the denticulate ligam ent.C.Spinal cord,spinalnerves,and spinal m eninges.The term “m ater” is often om itted,referring sim ply to “dura,” “arachnoid,” and “pia.” A total of 31 pairs of spinal nerves are attached to the spinal cord: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal (Fig. 2.17A). Multiple rootlets attach to the posterior and anterior surfaces of the spinal cord and converge to form posterior and anterior roots of the spinal nerves (Fig. 2.18). The part of the spinal cord to which the rootlets of one bilateral pair of roots attach is a segment of the spinal cord. The posterior roots of the spinal nerves contain afferent (or sensory) fibers from skin, subcutaneous and deep tissues, and, often, viscera. The anterior roots of spinal nerves contain efferent (motor) fibers to skeletal muscle, and many contain presynaptic autonomic fibers. The cell bodies of somatic axons contributing to the anterior roots are in the anterior horns of gray matter of the spinal cord (Fig. 2.18C), whereas the cell bodies of axons making up the posterior roots are outside the spinal cord in the spinal ganglia (posterior or dorsal root ganglia) at the distal ends of the posterior roots. The posterior and anterior nerve roots unite at their points of exit from the vertebral canal to form a spinal nerve. Each spinal nerve divides almost immediately into a posterior (dorsal) ramus and anterior (ventral) ramus (Fig. 2.18A). The posterior rami supply the zygapophysial joints, deep muscles of the back, and overlying skin; the anterior rami supply the muscles, joints, and skin of the limbs and the remainder of the trunk. 4  Describe the m ajor features ofthe spinalcord,m eninges,and Figure 2.19 m eningealspaces and their relationships within the vertebralcanal Spinalcord in situ: vasculature and m eninges w ith associated spaces.M ost proxim alspinalnerves and roots are accom panied by radicular arteries,w hich do not reach the posterior,anterior,or spinalarteries.Segm ental m edullary arteries occur irregularly in the place of radicular arteries— they are really justlarger vessels that m ake itallthe w ay to the spinal arteries.A.Vasculature ofspinal cord w ith m eninges.B. Vasculature ofspinalcord. Collectively, the dura mater, arachnoid mater, and pia mater surrounding the spinal cord forming the spinal meninges. These membranes and CSF (cerebrospinal fluid) surround, support, and protect the spinal cord and the spinal nerve roots, including those in the cauda equina. The spinal dura mater, composed of tough, fibrous, and some elastic tissue, is the outermost covering membrane of the spinal cord (Fig. 2.18). The spinal dura mater is separated from the vertebrae by the extradural (epidural) space and forms the spinal dural sac, a long tubular sheath within the vertebral canal (Fig. 2.17). The spinal dural sac is continuous with the cranial dura mater. The spinal dural sac is pierced by the spinal nerves and is anchored inferiorly to the coccyx by the filum terminale externum. 5  Describe the m ajor features ofthe spinalcord,m eninges,and Figure 2.19 m eningealspaces and their relationships within the vertebralcanal Continued. The spinal arachnoid mater is a membrane that lines the dural sac and the dural root sheaths. It encloses the CSF‐filled subarachnoid space containing the spinal cord, spinal nerve roots, and spinal ganglia (Figs. 2.18B, C and 2.19A). In a lumbar spinal puncture, the needle traverses the dura and arachnoid mater simultaneously. Bleeding into this layer creates a pathological space at the dura–arachnoid junction in which a subdural hematoma is formed. The spinal pia mater, the innermost covering membrane of the spinal cord, it also directly covers the roots of the spinal nerves and spinal blood vessels. Inferior to the conus medullaris, the pia continues as the filum terminale (Fig. 2.17B). The spinal cord is suspended in the dural sac by the filum terminale and especially by the right and left denticulate ligaments which run longitudinally along each side of the spinal cord. 6  Describe the m ajor features ofthe spinalcord,m eninges,and Table 2.4 m eningealspaces and their relationships within the vertebralcanal Spaces Associated w ith SpinalM eninges 7  Identify the nerve roottypically affected by herniated nucleus pulposus Figure 2.17 (intervertebraldisc)atany given vertebrallevelin the cervicalor lum bar spine. Relationship of vertebral colum n,spinalcord,and spinalnerves.A. Schem atic.B.Cauda equina.Note the relation ofthe spinalcord segm ents and spinal nerves to the vertebral colum n. Because there are 8 cervical spinal nerves (C1‐8) and only 7 cervical vertebrae (C1‐7), each cervical spinal nerve exits the vertebral column above the vertebra with the same number and spinal nerve C8 exits between vertebrae C7 and T1. For example, spinal nerve C1 exits the vertebral column above the C1 vertebra and spinal nerve C2 exits above the C2 vertebra. For the rest of the spinal cord each spinal nerve exits the vertebral column below the vertebra with the same number. For example, spinal nerve T1 exits the vertebral column below the T1 vertebra and spinal nerve L1 exits the vertebral column below the L1 vertebra. 8  Identify the nerve roottypically affected by herniated nucleus pulposus Figure B2.8 (intervertebraldisc)atany given vertebrallevelin the cervicalor lum bar spine. Herniation of nucleus pulposus. L4 L5 If degeneration of the posterior longitudinal ligament and wearing of the anulus fibrosus has occurred, the nucleus pulposus may herniate into the vertebral canal and compress the spinal cord or nerve roots of spinal nerves in the cauda equina (Fig. B2.8). Herniations usually occur posterolaterally, where the anulus is relatively thin and does not receive support from the posterior or anterior longitudinal ligaments. In the lumbar spine, the spinal nerve that exits a given IV foramen passes through the superior half of the foramen and thus lies above and is not affected by a herniating disc at that level while the nerve roots passing to the IV foramen below pass directly across the area of herniation (i.e., herniation of the L4–L5 disc affects the L5 nerve root) (Fig. B2.8D). In the cervical region, a herniating cervical disc compresses the spinal nerve exiting at that level (i.e., herniation of the C6‐C7 disc affects the C7 nerve root because the C7 nerve exits above the C7 vertebra). An easy way to remember the above is that the second number for the intervertebral disc that is herniated is also the number of the nerve typically affected. 9  Nam e the m ajor m uscles ofthe back and describe their actions, Figure 2.21 innervations (dorsalvs.ventralram i),and generalattachm ents. Distinguish intrinsic vs.extrinsic m uscle Transverse section of posterolateral abdom inalw all.The intrinsic back m uscles and layers ofthoracolum bar fascia are shown. There are two major groups of muscles in the back. The extrinsic back muscles include superficial and intermediate muscles that produce and control limb and respiratory movements, respectively, innervated by anterior rami of spinal nerves. These are covered in Upper Limb. The intrinsic back muscles (muscles of back proper, deep back muscles) are innervated by the posterior rami of spinal nerves and act to maintain posture and control movements of the vertebral column. The deep back muscles are grouped into superficial, intermediate, and deep layers according to their relationship to the surface (Table 2.5). 10  Nam e the m ajor m uscles ofthe back and describe their actions, Figure 2.22 innervations (dorsalvs.ventralram i),and generalattachm ents. Distinguish intrinsic vs.extrinsic m uscle Superficialand interm ediate layers of intrinsic back m uscles.A. Overview.B.Iliocostalis.C. Splenius capitis and splenius cervicis.D. Spinalis.E.Longissim us. The splenius cervicis and splenius capitis arise from the midline and extend superolaterally to the cervical vertebrae and cranium respectively (Fig. 2.22A, C). The erector spinae muscles (sacrospinalis) lie in a “groove” on each side of the vertebral column between the spinous processes and the angles of the ribs (Fig. 2.22). The massive erector spinae, the chief extensor of the vertebral column, divides into three muscle columns: Iliocostalis: lateral column Longissimus: intermediate column Spinalis: medial column Each column is divided regionally into three parts according to its superior attachments (e.g., iliocostalis lumborum, iliocostalis thoracis, and iliocostalis cervicis). 11  Nam e the m ajor m uscles ofthe back and describe their actions, Figure 2.23 innervations (dorsalvs.ventralram i),and generalattachm ents. Distinguish intrinsic vs.extrinsic m uscle Deep layer of intrinsic back m uscles.A.Overview.The transversospinales consists of three layers (sem ispinalis, m ultifidus,and rotatores).B. Transverse section showing relationships ofback m uscles. C.Sem ispinalis.D.M ultifidus.E. Rotatores.Also shown are the interspinales,intertransversarii, and levatores costarum. Deep to the erector spinae muscles is an obliquely oriented group of muscles—the transversospinales muscle group. These muscles originate from transverse processes of vertebrae and pass to spinous processes of more superior vertebrae. They occupy the “gutter” between the transverse and spinous processes (Fig. 2.23). The semispinalis is superficial, spanning four to six segments. The multifidus is deeper, spanning two to four segments. The rotatores are deepest, spanning one to two segments. 12  Nam e the m ajor m uscles ofthe back and describe their actions, Figure 2.26 innervations (dorsalvs.ventralram i),and generalattachm ents. Distinguish intrinsic vs.extrinsic m uscle Suboccipitalm uscles and suboccipitaltriangle. The suboccipital triangle lies deep to the trapezius and semispinalis capitis muscles. The four small muscles in the suboccipital region—rectus capitis posterior major and minor and obliquus capitis superior and inferior—are innervated by the posterior ramus of C1, the suboccipital nerve. The nerve emerges from the triangle while the vertebral artery courses deeply between the occipital bone and the atlas (C1 vertebra) within the suboccipital triangle. Rectus capitis posterior major arises from the spinous process of the C2 vertebra and inserts into the lateral part of the inferior nuchal line of the occipital bone. Rectus capitis posterior minor arises from the posterior tubercle on the posterior arch of the C1 vertebra and inserts into the medial third of the inferior nuchal line. Obliquus capitis inferior arises from the spinous process of the C2 vertebra and inserts into the transverse process of the C1 vertebra. The name of this muscle is somewhat misleading because it is the only “capitis” muscle that has no attachment to the cranium. Obliquus capitis superior arises from the transverse process of C1 and inserts into the occipital bone between the superior and the inferior nuchal lines. The actions of the suboccipital group of muscles are to extend the head on C1 and rotate the head and the C1 on C2 vertebrae. 13  Nam e the m ajor m uscles ofthe back and describe their actions, Figure 2.29 innervations (dorsalvs.ventralram i),and generalattachm ents. Distinguish intrinsic vs.extrinsic m uscle Innervation of suboccipitalregion and head.A.Dissection of nerves ofposterior cervicalregion.B.Sensory innervation. 14  Nam e the m ajor m uscles ofthe back and describe their actions, Table 2.10 innervations (dorsalvs.ventralram i),and generalattachm ents. Distinguish intrinsic vs.extrinsic m uscle Nerve Supply of Posterior Aspect of Head and Neck 15  Explain the difference betw een perform ing lum bar puncture Figure B2.11 and epiduralanesthesia Lum bar spinalpuncture and epiduralanesthesia. ( ) To obtain a sample of CSF from the lumbar cistern, a lumbar puncture needle is inserted into the subarachnoid space. Lumbar spinal puncture (spinal tap) is performed with the patient leaning forward or lying on the side with the back flexed. Flexion of the vertebral column facilitates insertion of the needle by spreading the laminae and spinous processes apart, stretching the ligament flava (Fig. B2.11). The needle is inserted in the midline between the spinous processes of the L3 and L4 (or the L4 and L5) vertebrae. At these levels in adults, there is reduced danger of damaging the spinal cord. In a lumbar spinal puncture, the needle traverses the dura and arachnoid mater simultaneously. The order of structures pierced, from superficial to deep is: skin  supraspinous ligament  interspinous ligament  ligamentum flavum  dura mater  arachnoid mater. 16  Explain the difference betw een perform ing lum bar puncture Figure B2.12 and epiduralanesthesia Trans-sacraland caudal anesthesia. An anesthetic agent can be injected into the lumbar extradural (epidural) space using the position described for lumbar spinal puncture (Fig. B2.11). The anesthetic has a direct effect on the spinal nerve roots of the cauda equina after they exit from the dural sac (Fig. B2.12). The patient loses sensation inferior to the level of the block. In this case, the order of structures pierced, from superficial to deep is: skin  supraspinous ligament  interspinous ligament  ligamentum flavum. An anesthetic agent can also be injected into the extradural space in the sacral canal through the sacral hiatus (caudal epidural anesthesia) or through the posterior sacral foramina (trans‐sacral epidural anesthesia) (Fig. B2.12). 17  Describe the osteological features of the bones of the upper extremity. Figure 3.1 Segments and bones of upper limb. The upper limb is divided into four main segments: shoulder, arm, forearm, and hand. The upper limb consists of four segments, which are further subdivided into regions (Figs. 3.1 and 3.2): The pectoral (shoulder) girdle is a bony ring, incomplete posteriorly, formed by the scapulae and clavicles and completed anteriorly by the manubrium of the sternum. Shoulder, which includes the deltoid, pectoral, scapular, and lateral part of lateral cervical region. Arm (L. brachium) is between the shoulder and the elbow and is centered around the humerus, it consists of the anterior and posterior regions. Forearm (L. antebrachium) is between the elbow and the wrist and contains the ulna and the radius, it consists of the anterior and posterior regions. Hand (L. manus) is distal to the forearm and contains the carpus, metacarpus, and phalanges [wrist, palm, dorsum of hand, and digits (fingers, including the opposable thumb)].  Describe the osteological features of the bones of the upper extremity. Figure 3.3 Clavicle. A. Inferior surface. B. Superior surface. C. Articulations of clavicle. The clavicle (collar bone) connects the upper limb to the trunk. Its sternal end articulates with the manubrium of the sternum at the sternoclavicular (SC) joint. Its acromial end articulates with the acromion of the scapula at the acromioclavicular (AC) joint (Figs. 3.3 and 3.4). The medial two thirds of the shaft of the clavicle are convex anteriorly, whereas the lateral third is flattened and concave anteriorly. These curvatures increase the resilience of the clavicle and give it the appearance of an elongated capital S.  Describe the osteological features of the bones of the upper extremity. Figure 3.4 Bones of upper limb. A. Anterior aspect of articulated upper limb. The scapula (shoulder blade) is a triangular flat bone that lies on the posterolateral aspect of the thorax, overlying the 2nd through 7th ribs (Figs. 3.3 and 3.4). The convex posterior surface of the scapula is unevenly divided by the spine of the scapula into a small supraspinous fossa and a much larger infraspinous fossa. The concave costal surface of the scapula has a large subscapular fossa. The scapula has medial (axillary), lateral (vertebral), and superior borders and superior and inferior angles. The lateral border of scapula is the thickest part of the bone, which, superiorly, includes the head of the scapula where the glenoid cavity is located. The neck of the scapula is just medial to the head (Fig. 3.4B). The superior border of the scapula is marked near the junction of its medial two thirds and lateral third by the suprascapular notch. The spine of the scapula continues laterally, expanding to form the acromion, the subcutaneous point of the shoulder that articulates with the acromial end of the clavicle (Fig. 3.3C).  Describe the osteological features of the bones of the upper extremity. Figure 3.5 Right scapula. Superolaterally, the lateral surface of the head of the scapula has a glenoid cavity, which articulates with the head of the humerus at the glenohumeral (shoulder) joint (Fig. 3.5). The glenoid (G. socket) cavity is a shallow, concave, oval fossa, which is directed anterolaterally and slightly superiorly and is considerably smaller than the head of the humerus for which it serves as a socket. The beak‐like coracoid process is superior to the glenoid cavity and projects anterolaterally.  Describe the osteological features of the bones of the upper extremity. Figure 3.4 (continued) Bones of upper limb. B. Posterior aspect of articulated upper limb. The humerus (arm bone), the largest bone in the upper limb, articulates with the scapula at the glenohumeral joint and the radius and the ulna at the elbow joint (Fig. 3.4). Proximally, the ball‐shaped head of the humerus articulates with the glenoid cavity of the scapula. The intertubercular sulcus (bicipital groove) of the proximal end of the humerus separates the lesser tubercle from the greater tubercle. Just distal to the humeral head, the anatomical neck of the humerus separates the head from the tubercles. Distal to the tubercles is the narrow surgical neck of the humerus. The shaft of the humerus has two prominent features: the deltoid tuberosity laterally and the radial groove (groove for radial nerve, spiral groove) posteriorly for the radial nerve and profunda brachii artery. The inferior end of the humeral shaft widens as the sharp medial and lateral supracondylar ridges form and then end distally in the prominent medial epicondyle and lateral epicondyle.  Describe the osteological features of the bones of the upper extremity. Figure 3.4 (continued) Bones of upper limb. A. Anterior aspect of articulated upper limb. The distal end of the humerus, including the trochlea, capitulum, olecranon, coronoid, and radial fossae, makes up the condyle of the humerus. It has two articular surfaces: a lateral capitulum (L. little head) for articulation with the head of the radius and a medial trochlea (L. pulley) for articulation with the trochlear notch of the ulna. Superior to the trochlea anteriorly is the coronoid fossa, which receives the coronoid process of the ulna during full flexion of the elbow (Figs. 3.4A and 3.6). Posteriorly, the olecranon fossa accommodates the olecranon of the ulna during extension of the elbow. Superior to the capitulum anteriorly, the shallow radial fossa accommodates the edge of the head of the radius when the elbow is fully flexed.  Describe the osteological features of the bones of the upper extremity. Figure 3.7 Ulna and radius. A. Proximal end of ulna. B. Distal end of radius. The ulna, the stabilizing bone of the forearm, is the medial and longer of the two forearm bones (Fig. 3.4). Its proximal end has two prominent projections—the olecranon posteriorly and the coronoid process anteriorly; they form the walls of the trochlear notch. The trochlear notch of the ulna articulates with the trochlea of the humerus. Inferior to the coronoid process is the tuberosity of the ulna. On the lateral side of the coronoid process is a smooth, rounded concavity, the radial notch, which articulates with the head of radius (Fig. 3.7A). Distal to the radial notch is a prominent ridge, the supinator crest, and between it and the distal part of the coronoid process is a concavity, the supinator fossa. Proximally, the shaft of the ulna is thick, but it tapers, diminishing in diameter distally. At its narrow distal end is the rounded head of ulna with the small, conical ulnar styloid process (Fig. 3.4). The ulna does not articulate directly with the carpal bones. It is separated from the carpals by a fibrocartilaginous articular disc.  Describe the osteological features of the bones of the upper extremity. Figure 3.4 (continued) Bones of upper limb. A. Anterior aspect of articulated upper limb. The radius is the lateral and shorter of the two forearm bones. Its proximal end consists of a cylindrical head, a short neck, and a projection from the medial surface, the radial tuberosity (Fig. 3.4A). Proximally, the smooth superior aspect of the head of the radius is concave for articulation with the capitulum of humerus. The head also articulates medially with the radial notch of ulna (Fig. 3.7A). The neck of the radius is the narrow part between the head and the radial tuberosity. The radial tuberosity demarcates the proximal end (head and neck) from the shaft. The shaft of the radius has a lateral convexity and gradually enlarges as it passes distally. The medial aspect of the distal end of the radius forms a concavity, the ulnar notch, which accommodates the head of the ulna (Fig. 3.7B). Its lateral aspect terminates distally as the radial styloid process. The radial styloid process is larger than the ulnar styloid process and extends farther distally. This relationship is clinically important when the ulna and/or radius is fractured (see Fig. B3.3). The dorsal tubercle of the radius lies between two of the shallow grooves for passage of the tendons of forearm muscles and serves as a trochlea (pulley) for the tendon of the long extensor of the thumb.  Describe the osteological features of the bones of the upper extremity. Figure 3.8 Bones of hand. The wrist, or carpus, is composed of eight carpal bones (carpals) arranged in proximal and distal rows of four (Figs. 3.8 and 3.9). These small bones give flexibility to the wrist. From lateral to medial, the four bones in the proximal row of carpals are as follows: Scaphoid (G. skaphé, skiff, boat): a boat‐shaped bone that has a prominent scaphoid tubercle Lunate (L. luna, moon): a moon‐shaped bone that is broader anteriorly than posteriorly Triquetrum (L. triquetrus, three‐cornered): a pyramidal bone on the medial aspect of the carpus Pisiform (L. pisum, pea): a small, pea‐shaped bone that lies on the palmar surface of the triquetrum The proximal surfaces of the distal row of carpals articulate with the proximal row of carpals, and their distal surfaces articulate with the metacarpals. From lateral to medial, the four bones in the distal row of carpals are as follows: Trapezium (G. trapeze, table): a four‐sided bone on the lateral side of the carpus Trapezoid: a wedge‐shaped bone Capitate (L. caput, head): the head‐shaped bone that is the largest bone in the carpus Hamate (L. hamulus, little hook): a wedge‐shaped bone, which has a hooked process, the hook of hamate, that extends anteriorly  Describe the osteological features of the bones of the upper extremity. Figure 3.9 Radiograph of right hand. The metacarpus forms the skeleton of the palm of the hand between the carpus and the phalanges (Fig. 3.9). It is composed of five metacarpal bones (metacarpals). Each of these bones consists of a base, a shaft, and a head. The proximal bases of the metacarpals articulate with the carpal bones, and the distal heads of the metacarpals articulate with the proximal phalanges and form the knuckles. The 1st metacarpal (of the thumb) is the thickest and shortest of these bones. Each digit has three phalanges (proximal, middle, and distal) except for the first (thumb), which has only two (proximal and distal). Each phalanx has a base proximally, a shaft (body), and a head distally. The distal phalanges are flattened and expanded at their distal ends, which underlie the nail beds.  Identify the surface anatomy and palpable bony landmarks of the upper extremity. Figure SA3.1 Surface projection and palpable features of bones of upper limb. A. Overview.  Describe the venous and lymphatic drainage and arterial supply of the upper extremity. Figure 3.11 Superficial venous and lymphatic drainage of upper limb. A. Cephalic and basilic veins, lymphatic vessels, and lymph nodes. B. Dorsal venous arch and lymphatic drainage of dorsum of hand. Green arrows, superficial lymphatic drainage to lymph nodes. Superficial lymphatic vessels arise from lymphatic plexuses in the skin of the fingers, palm, and dorsum of the hand and ascend mostly with superficial veins, such as the cephalic and basilic veins (Fig. 3.11). Some lymphatic vessels accompanying the basilic vein enter the cubital lymph nodes located proximal to the medial epicondyle. Efferent vessels from these nodes ascend in the arm and terminate in the humeral (lateral) axillary lymph nodes. Most lymphatic vessels accompanying the cephalic vein cross the proximal part of the arm and anterior aspect of the shoulder to enter the apical axillary lymph nodes. The main superficial veins of the upper limb, the cephalic and basilic veins, originate in the subcutaneous tissue on the dorsum of the hand from the dorsal venous network (Fig. 3.11). Perforating veins form communications between the superficial and the deep veins.  Describe the venous and lymphatic drainage and arterial supply of the upper extremity. Figure 3.11 (continued) Superficial venous and lymphatic drainage of upper limb. A. Cephalic and basilic veins, lymphatic vessels, and lymph nodes. B. Dorsal venous arch and lymphatic drainage of dorsum of hand. Green arrows, superficial lymphatic drainage to lymph nodes. The cephalic vein (G. kephalé, head) ascends in the subcutaneous tissue from the lateral aspect of the dorsal venous network, proceeding along the lateral border of the wrist and the anterolateral surface of the forearm and arm. Anterior to the elbow, the cephalic vein communicates with the median cubital vein, which passes obliquely across the anterior aspect of the elbow and joins the basilic vein. Superiorly, the cephalic vein passes between the deltoid and the pectoralis major muscles and enters the clavipectoral triangle, where it pierces the clavipectoral fascia, and joins the terminal part of the axillary vein. The basilic vein ascends in the subcutaneous tissue from the medial end of the dorsal venous network along the medial side of the forearm and inferior part of the arm. It then passes deeply near the junction of the middle and inferior thirds of the arm and running superiorly parallel to the brachial artery, where it merges with the accompanying veins (L. venae comitantes) of the brachial artery (i.e. brachial veins) to form the axillary vein (Fig. 3.11A). The median antebrachial cutaneous vein (median vein of forearm) ascends in the middle of the anterior aspect of the forearm.  Describe the venous and lymphatic drainage and arterial supply of the upper extremity. Figure 3.12 Deep veins of upper limb. Deep veins of limbs bear the same name as the arteries they accompany. Deep veins lie internal to the deep fascia and usually occur as paired, continually anastomosing, accompanying veins that travel with and bear the same name as the major arteries of the upper limb (Fig. 3.12).  Describe the venous and lymphatic drainage and arterial supply of the upper extremity. Figure 3.13 Arterial supply and sites of palpation of pulses of upper limb. The axillary artery, the main blood supply to the upper limb (Fig. 3.13) is the continuation of the subclavian artery distal to the lateral border of the 1st rib. The axillary artery becomes the brachial artery at the inferior border of the teres major and ends in the cubital fossa opposite the neck of the radius, where it divides into the radial and ulnar arteries. A major branch of the brachial artery is the profunda brachii artery (deep artery of arm) that travels posterior to the humerus in the radial groove and helps form the periarticular cubital anastomosis of the elbow region. The ulnar artery descends through the anterior compartment of the forearm. The radial artery courses through the forearm laterally deep to the brachioradialis and leaves the forearm by coursing around the lateral aspect of the wrist and crossing the floor of the anatomical snuff box to reach the hand. The ulnar and radial arteries and their branches provide all the blood to the hand primarily via the superficial and deep palmar arches.  Distinguish the innervation of the upper extremity with respect to dermatomes and peripheral nerve distribution. Figure 3.14 Peripheral (cutaneous) innervation of upper limb. Cutaneous nerves in the subcutaneous tissue supply the skin of the upper limb (Fig. 3.14). You do not need to memorize nerve root levels, but you should be able to determine which area in the diagram above would be affected by damage to a terminal branch of the brachial plexus.  Distinguish the innervation of the upper extremity with respect to dermatomes and peripheral nerve distribution. Figure 3.15 Segmental (dermatomal) innervation. The area of skin supplied by cutaneous branches from a single spinal nerve is a dermatome (Fig. 3.15). The dermatomes of the limb follow a general pattern that is easy to understand if one notes that developmentally, the limbs grow as lateral protrusions of the trunk, with the 1st digit (thumb or great toe) located on the cranial side. Thus, the lateral surface of the upper limb is more cranial than the medial surface.  Distinguish the innervation of the upper extremity with respect to dermatomes and peripheral nerve distribution. Figure 3.16 Segmental innervation of movements of upper limb. The unilateral embryological muscle mass receiving innervation from a single spinal cord segment or spinal nerve comprises a myotome. Upper limb muscles usually receive motor fibers from several spinal cord segments via multisegmental (named) peripheral nerves. Thus, most muscles include more than one myotome, and most often, multiple spinal cord segments are involved in producing the movements. The muscle myotomes are grouped by joint movement to facilitate clinical testing (Fig. 3.16; Table 3.1). The information above is summarized sufficiently in the chart on the next slide. Table 3.1 Distinguish the innervation of the upper extremity with respect to dermatomes and peripheral nerve distribution. Upper Limb Myotomes: Primary Segments  Distinguish the innervation of the upper extremity with respect to dermatomes and peripheral nerve distribution. Figure 3.17 Overview of peripheral nerves innervating upper limb. A. Musculocutaneous nerve. B. Median nerve. The same mixed multisegmental peripheral nerves that convey sensory fibers to the skin, muscles, and joints of the upper limb convey somatic motor (general somatic efferent) fibers to the upper limb muscles. The somatic (peripheral) motor and sensory innervation of the upper limb by the musculocutaneous, median, ulnar, axillary, and radial nerves is summarized in Figure 3.17.  Distinguish the innervation of the upper extremity with respect to dermatomes and peripheral nerve distribution. Figure 3.17 (continued) Overview of peripheral nerves innervating upper limb. C. Axillary nerve. D. Ulnar nerve. E. Radial nerve.  Describe surgical neck, mid‐shaft, and distal fractures of the humerus and recognize neurovascular structures at risk with each. Figure B3.2 Fractures of humerus. Fractures of the surgical neck of the humerus are especially common in elderly people with osteoporosis (Fig. B3.2A). Even a low‐energy fall on the hand, with the force being transmitted up the forearm bones of the extended limb, may result in a fracture. Transverse fractures of the shaft of humerus frequently result from a direct blow to the arm. Fracture of the distal part of the humerus, near the supraepicondylar ridges, is a supraepicondylar (supracondylar) fracture. Because nerves are in contact with the humerus, they may be injured when the associated part of the humerus is fractured: surgical neck, axillary nerve; radial groove, radial nerve; distal humerus, median nerve; and medial epicondyle, ulnar nerve (Fig. B3.2B).  Describe Colles and scaphoid fractures, including radiographs. Figure B3.3 Colles fracture with a dinner fork deformity. Fractures of both the ulna and the radius are the result of severe injury. A direct injury usually produces transverse fractures at the same level, often in the middle third of the bones. Because the shafts of these bones are firmly bound together by the interosseous membrane, a fracture of one bone is likely to be associated with dislocation of the nearest joint. Fracture of the distal end or the radius is the most common fracture in people older than 50 years of age. A complete fracture of the distal 2 cm of the radius, called a Colles fracture, is the most common fracture of the forearm (Fig. B3.3). The distal fragment of the radius is displaced dorsally and often comminuted (broken into pieces) and results from forced dorsiflexion of the hand, usually as the result of trying to ease a fall by outstretching the upper limb. Often, the ulnar styloid process is avulsed (broken off). Normally, the radial styloid process projects farther distally than the ulnar styloid process; consequently, when a Colles fracture occurs, this relationship is reversed because of shortening of the radius. This fracture is often referred to as a dinner fork (silver fork) deformity because a posterior angulation occurs in the forearm just proximal to the wrist and the normal anterior curvature of the relaxed hand. The posterior bending is produced by the posterior displacement and tilt of the distal fragment of the radius.  Describe Colles and scaphoid fractures, including radiographs. Figure B3.4 Radiographs of fracture of scaphoid (S). Fracture of the scaphoid often results from a fall on the palm with the hand abducted. The fracture occurs across the narrow part (“waist”) of the scaphoid. Pain occurs primarily on the lateral side of the wrist, especially during dorsiflexion and abduction of the hand. Owing to the poor blood supply to the proximal part of the scaphoid, union of the fractured parts may take several months. Avascular necrosis of the proximal fragment of the scaphoid (pathological death of bone resulting from poor blood supply) may occur (Fig. B3.4B) and produce degenerative joint disease of the wrist.  Describe the extrinsic (superficial) m uscles of the back and Figure 3.18 pectoralregion in term s of their generalattachm ents, innervations,and m ajor actions. Anterior axioappendicular m uscles.A.Superficial dissection ofpectoral region.B.Pectoralis m ajor. C.Serratus anterior.Inset, scapular attachm entof serratus anterior (blue).D. Pectoralis m inor and subclavius. Axioappendicular muscles (extrinsic shoulder muscles) attach the superior appendicular skeleton of the upper limb to the axial skeleton (vertebral column); most act at the physiological scapulothoracic joint, moving the scapula on the chest wall. Scapulohumeral muscles (intrinsic shoulder muscles) attach the scapula to the humerus and act at the glenohumeral (shoulder) joint. Four anterior axioappendicular (thoracoappendicular or pectoral) muscles move the pectoral girdle: pectoralis major, pectoralis minor, subclavius, and serratus anterior (Fig. 3.18, 3.19, Table 3.2 ).  Describe the extrinsic (superficial) m uscles of the back and Table 3.2 pectoralregion in term s of their generalattachm ents, innervations,and m ajor actions. Anterior Axioappendicular M uscles The fan‐shaped pectoralis major has clavicular and sternocostal heads (Fig. 3.18B). The pectoralis major and adjacent deltoid form the narrow deltopectoral groove, in which the cephalic vein runs. However, the muscles diverge slightly from each other superiorly and, along with the clavicle, form the clavipectoral (deltopectoral) triangle (Fig. 3.18A). The triangular pectoralis minor lies in the anterior wall of the axilla (Fig. 3.18D), where it is almost completely covered by the pectoralis major. The pectoralis minor stabilizes the scapula and is used when stretching the upper limb forward to touch an object that is just out of reach. With the coracoid process, the pectoralis minor forms a “bridge” under which vessels and nerves pass to the arm. *There is no need to learn nerve root levels for innervation, just the nerves. Focus primarily on innervation and action.  Describe the extrinsic (superficial) m uscles of the back and Figure 3.19 pectoralregion in term s of their generalattachm ents, innervations,and m ajor actions. Attachm ents of anterior axioappendicular m uscles. The subclavius lies almost horizontally when the arm is in the anatomical position (Fig. 3.18D). This small, round muscle is located inferior to the clavicle and affords some protection to the subclavian vessels and the superior trunk of the brachial plexus if the clavicle fractures. The serratus anterior overlies the lateral part of the thorax and forms the medial wall of the axilla (Fig. 3.18C). This broad sheet of thick muscle was given its name because of the sawtooth appearance of its fleshy slips or digitations (L. serratus, a saw). By keeping the scapula closely applied to the thoracic wall, the serratus anterior anchors this bone, enabling other muscles to use it as a fixed bone for movements of the humerus.  Describe the extrinsic (superficial) m uscles of the back and Figure B3.5 pectoralregion in term s of their generalattachm ents, innervations,and m ajor actions. W inged scapula. When the serratus anterior is paralyzed because of injury to the long thoracic nerve, the medial border of the scapula moves laterally and posteriorly away from the thoracic wall. This gives the scapula the appearance of a wing. When the arm is raised, the medial border and inferior angle of the scapula pull markedly away from the posterior thoracic wall, a deformation known as a winged scapula (Fig. B3.5). The arm cannot be abducted above the horizontal position because the serratus anterior is unable to rotate the glenoid cavity superiorly to allow complete abduction of the limb.  Describe the extrinsic (superficial) m uscles of the back and Figure 3.20 pectoralregion in term s of their generalattachm ents, innervations,and m ajor actions. Posterior axioappendicular m uscles.A.Overview.B and C.Bony attachm ents. The posterior axioappendicular muscles (also described as superficial extrinsic back muscles) are divided into two groups: Superficial posterior axioappendicular muscles: trapezius and latissimus dorsi Deep posterior axioappendicular muscles: levator scapulae and rhomboids  Describe the extrinsic (superficial) m uscles of the back and pectoralregion Table 3.3 in term s of their generalattachm ents,innervations,and m ajor actions. Posterior Axioappendicular M uscles *Focus primarily on innervation and action, but have a general idea of attachments (e.g., the levator scapulae attach to the transverse processes of C1‐4 and the medial border of the scapula).  Describe the extrinsic (superficial) m uscles of the back and Figure 3.21 pectoralregion in term s of their generalattachm ents, innervations,and m ajor actions. Scapulohum eralm uscles. A and C.Bony attachm ents.B. Supraspinatus, infraspinatus,and teres m inor.D.Deltoid m uscle. A,acrom ialpart;C, clavicular part;S,spinal part.E.Subscapularis. Four of the scapulohumeral muscles (intrinsic shoulder muscles) ‐ Supraspinatus, Infraspinatus, Teres minor, and Subscapularis (referred to as SITS muscles) ‐ are called rotator cuff muscles because they form a musculotendinous rotator cuff around the glenohumeral joint. All except the supraspinatus are rotators of the humerus. The supraspinatus initiates and assists the deltoid in the first 15° of abduction of the arm. The tendons of the SITS or rotator cuff muscles blend with the joint capsule of the glenohumeral joint, reinforcing it as the musculotendinous rotator cuff, which protects the joint and gives it stability. Tonic contraction of these muscles holds the relatively large head of the humerus firmly against the small and shallow glenoid cavity during arm movements.  Describe the extrinsic (superficial) m uscles of the back and pectoralregion Table 3.4 in term s of their generalattachm ents,innervations,and m ajor actions. Scapulohum eral (Intrinsic Shoulder) M uscles Injury to Axillary Nerve Atrophy of the deltoid occurs when the axillary nerve (C5 and C6) is severely damaged (e.g., as might occur when the surgical neck of the humerus is fractured). A loss of sensation may occur over the lateral side of the proximal part of the arm, the area supplied by the superior lateral cutaneous nerve of the arm and there may be weakness in shoulder abduction. To test the deltoid (or the function of the axillary nerve), the arm is abducted, against resistance, starting from approximately 15°.  Describe the course and branches of the axillary artery and Figure 3.22 vein,and drainage pattern of axillary lym ph nodes. Location and boundaries of axilla. The axilla is the pyramidal compartment inferior to the glenohumeral joint. The shape and size of the axilla vary depending on the position of the arm; it almost disappears when the shoulder joint is fully abducted. The axilla provides a passageway for vessels and nerves going to and from the upper limb.  Describe the course and branches of the axillary artery and Figure 3.23 vein,and drainage pattern of axillary lym ph nodes. Arteries of shoulder region and arm.A. Overview.B.Scapular anastom osis. The axillary artery begins at the lateral border of the 1st rib as the continuation of the subclavian artery and ends at the inferior border of the teres major (Fig. 3.23). It passes posterior to the pectoralis minor into the arm and becomes the brachial artery when it passes distal to the inferior border of the teres major. For descriptive purposes, the axillary artery is divided into three parts relative to the pectoralis minor (the part number also indicates the number of its branches): The first part of the axillary artery is located between the lateral border of the 1st rib and the medial border of the pectoralis minor; it has one branch: the superior thoracic artery. The second part of the axillary artery lies posterior to the pectoralis minor and has two branches: the thoracoacromial artery and lateral thoracic artery, which pass medial and lateral to the muscle, respectively. The third part of the axillary artery extends from the lateral border of the pectoralis minor to the inferior border of the teres major and has three branches. The subscapular artery is the largest branch of the axillary artery. Opposite the origin of this artery, the anterior circumflex humeral artery and posterior circumflex humeral artery arise.  Describe the course and branches of the axillary artery and Figure 3.24 vein,and drainage pattern of axillary lym ph nodes. Proxim alupper lim b veins,axillary lym ph nodes,and lym phatic drainage of upper lim b and breast. The axillary vein is formed by the union of the accompanying brachial veins and the basilic vein at the inferior border of the teres major (see Fig. 3.11A), it ends at the lateral border of the 1st rib, where it becomes the subclavian vein (Fig. 3.24).  Describe the course and branches of the axillary artery and Figure 3.25 vein,and drainage pattern of axillary lym ph nodes. Location and drainage pattern of axillary lym ph nodes. Apical lymph nodes receive lymph from the other axillary lymph nodes and drain into supraclavicular nodes and then into the subclavian lymphatic trunk. The subclavian lymphatic trunk may then drain into the right lymphatic duct or directly into the right venous angle (the right angle created by the union of the right internal jugular vein and the right subclavian vein as they form the right brachiocephalic vein). On the left side, the subclavian trunk commonly drains into the thoracic duct. 13  Describe the form ation of the brachialplexus Figure 3.26 including supra and infraclavicular branches. Brachialplexus and subclavian vessels in lateralcervicalregion (posterior triangle of neck). The brachial plexus is a major network of nerves supplying the upper limb which begins in the lateral cervical region and extends into the axilla. The brachial plexus is formed by the union of the anterior rami of the C5–T1 nerves, which constitute the roots of brachial plexus (Fig. 3.26; Table 3.6). The roots usually pass through the gap between the anterior and middle scalene muscles with the subclavian artery.  Describe the form ation of the brachialplexus Figure 3.27 including supra and infraclavicular branches. Brachialplexus. In the inferior part of the neck, the roots of the brachial plexus unite to form three trunks (Figs. 3.27 and 3.28): A superior trunk, from the union of the C5 and C6 roots A middle trunk, which is a continuation of the C7 root An inferior trunk, from the union of the C8 and T1 roots Each trunk of the brachial plexus divides into anterior and posterior divisions as the plexus passes through the cervicoaxillary canal posterior to the clavicle. Anterior divisions of the trunks supply the anterior (flexor) compartments of the upper limb, and posterior divisions of the trunks supply the posterior (extensor) compartments of the upper limb. The divisions of the trunks form three cords (lateral cord, medial cord, and posterior cord) of the brachial plexus within the axilla (Figs. 3.27 and 3.28C): The cords of the brachial plexus are named for their position in relation to the second part of the axillary artery (e.g., the lateral cord is lateral to the axillary artery, most easily seen when the limb is abducted).  Describe the form ation of the brachialplexus Figure 3.27 including supra and infraclavicular branches. Brachialplexus (continued). The brachial plexus is divided into supraclavicular and infraclavicular parts by the clavicle (Figs. 3.27 and 3.28; Table 3.6): Four branches of the supraclavicular part of the plexus arise from the roots (anterior rami) and trunks of the plexus (dorsal scapular nerve, long thoracic nerve, nerve to the subclavius, and suprascapular nerve) and are approachable through the neck. Branches of the infraclavicular part of the plexus arise from the cords of the brachial plexus; musculocutaneous nerve, axillary nerve, median nerve, radial nerve, and ulnar nerve.  Describe the form ation of the brachialplexus Figure 3.28 including supra and infraclavicular branches. Boundaries and contents of axilla.A.Relationship ofnerves and vessels to pectoralis m inor.B. Contents ofaxilla, transverse section.  Describe the form ation of the brachialplexus Figure 3.28 (continued) including supra and infraclavicular branches. Boundaries and contents of axilla.C.Form ation of brachialplexus.D. Posterior wallofaxilla with posterior cord of brachialplexus and its branches.  Describe the form ation of the brachialplexus Brachialplexus. including supra and infraclavicular branches. Understanding the brachialplexus from a developm ental perspective m ay be helpful. C8 Fig. A, Ventral aspect of the limb bud early in the fifth week of development. At this stage, the dermatomal pattern shows a simple segmental arrangement. Fig. B, Similar view later in the fifth week shows the modified arrangement of dermatomes. At this stage, the C5‐T1 nerve roots have merged, as the limb elongates, forming the brachial plexus. Fig. C, The dermatomal pattern in the adult upper limb. While the brachial plexus remains in the axilla, the terminal branches continued to elongate with the limb. Each terminal branch (peripheral nerve) carries fibers from the original spinal nerves that were mixed into it. For example, the median, radial, and ulnar nerves all carry motor and sensory C7 and C8 fibers to the hand, the C7 dermatome is the area of skin supplied by those original C7 fibers sensory fibers and the C8 dermatome is the area of skin supplied by the original C8 sensory fibers (also see Fig. 3.14). The muscle groups supplied by the original spinal nerve motor fibers are known as myotomes.  Describe the functionaldeficits resulting from Figure B3.6 injury to the superior and inferior brachialplexus as w ellas the term inalbranches. Brachialplexus injuries. Injuries to superior parts of the brachial plexus (C5 and C6) usually result from an excessive increase in the angle between the neck and the shoulder. These injuries can occur in a person who is thrown from a motorcycle or a horse and lands on the shoulder in a way that widely separates the neck and shoulder (Fig. B3.6A). This stretches or ruptures superior parts of the brachial plexus or avulses (tears) the roots of the plexus from the spinal cord. Injury to the superior trunk is apparent by the characteristic position of the limb (waiter’s tip position) in which the limb hangs by the side in medial rotation (Fig. B3.6B). Upper brachial plexus injuries can also occur in a newborn when excessive stretching of the neck occurs during delivery (Fig. B3.6C). As a result of injuries to the superior parts of the brachial plexus (Erb‐Duchenne palsy), paralysis of the muscles of the shoulder and arm supplied by C5–C6 occurs. The usual clinical appearance is an upper limb with an adducted shoulder, medially rotated arm, and extended elbow. The lateral aspect of the upper limb also experiences loss of sensation. 20  Describe the functionaldeficits resulting from Figure B3.6 injury to the superior and inferior brachialplexus as w ellas the term inalbranches. Brachialplexus injuries. Injuries to inferior parts of the brachial plexus (Klumpke paralysis) are much less common. These injuries may occur when the upper limb is suddenly pulled superiorly—for example, when a person grasps something to break a fall or when a baby’s limb is pulled excessively during delivery (Fig. B3.6D, E). These events injure the inferior trunk of the plexus (C8 and T1) and may avulse the roots of the spinal nerves from the spinal cord. The short muscles of the hand are affected and a claw hand results (Fig. B3.6F). 21  Describe the m uscles of the arm in term s of their general Figure 3.29 attachm ents,innervations,and m ajor actions. M uscles,arteries,and nerves of anterior arm. Of the four arm muscles, three flexors (biceps brachii, brachialis, and coracobrachialis) are in the anterior (flexor) compartment and are supplied by the musculocutaneous nerve (Figs. 3.28A and 3.29). The musculocutaneous nerve is a terminal branch of the lateral cord, which is formed by the anterior divisions of the superior and middle trunks (see Fig. 3.27). One three‐headed extensor muscle (triceps brachii) is in the posterior (extensor) compartment, supplied by the radial nerve. The radial nerve is a terminal branch of the posterior cord, which is formed by the posterior divisions of all three trunks (see Fig.3.27) A small triangular muscle on the posterior aspect of the elbow, the anconeus, covers the posterior aspect of the ulna proximally.  Describe the form ation of the brachialplexus Figure 3.27 including supra and infraclavicular branches. Brachialplexus,as a rem inder! In the inferior part of the neck, the roots of the brachial plexus unite to form three trunks (Figs. 3.27 and 3.28): A superior trunk, from the union of the C5 and C6 roots A middle trunk, which is a continuation of the C7 root An inferior trunk, from the union of the C8 and T1 roots Each trunk of the brachial plexus divides into anterior and posterior divisions as the plexus passes through the cervicoaxillary canal posterior to the clavicle. Anterior divisions of the trunks supply the anterior (flexor) compartments of the upper limb, and posterior divisions of the trunks supply the posterior (extensor) compartments of the upper limb. The divisions of the trunks form three cords (lateral cord, medial cord, and posterior cord) of the brachial plexus within the axilla (Figs. 3.27 and 3.28C): The cords of the brachial plexus are named for their position in relation to the second part of the axillary artery (e.g., the lateral cord is lateral to the axillary artery, most easily seen when the limb is abducted).  Describe the m uscles of the arm in term s of their general Figure 3.30 attachm ents,innervations,and m ajor actions. M uscles of arm and bony attachm ents. The biceps brachii has two heads: a long head and a short head. A broad band, the transverse humeral ligament, passes from the lesser to the greater tubercle of the humerus and converts the intertubercular groove into a canal for the tendon of the long head of the biceps. A triangular membranous band, the bicipital aponeurosis (Figs. 3.29 and 3.30B), runs from the biceps tendon across the cubital fossa and merges with the antebrachial (deep) fascia covering the flexor muscles in the medial side of the forearm. The brachialis, a flattened fusiform muscle, lies posterior (deep) to the biceps (Fig. 3.30B). The coracobrachialis, an elongated muscle in the superomedial part of the arm, the musculocutaneous nerve pierces it. The triceps brachii is a large fusiform muscle in the posterior compartment of the arm that has long, lateral, and medial heads (Figs. 3.30E and 3.31; Table 3.7). The triceps is the chief extensor of the elbow.  Describe the m uscles of the arm in term s of their general Table 3.7 attachm ents,innervations,and m ajor actions. M uscles of Arm  Describe the arteries,veins,and nerves of the arm. Figure 3.31 M uscles,arteries,and nerves of posterior arm. A.Superficialdissection.B. Deep dissection.C. Transverse section.D. Relationship ofarteries and nerves to hum erus. The brachial artery provides the main arterial supply to the arm and is the continuation of the axillary artery (Figs. 3.29, 3.31D, and 3.32; Table 3.5). It begins at the inferior border of the teres major and ends in the cubital fossa opposite the neck of the radius under cover of the bicipital aponeurosis, where it divides into the radial and ulnar arteries.  Describe the arteries,veins,and nerves of the arm. Figure 3.32 M uscles and neurovascular structures of arm. During its inferolateral course, the brachial artery accompanies the median nerve, which crosses anterior to the artery. The main named branches of the brachial artery that arise from its medial aspect are the profunda brachii artery (deep artery of arm) (Fig. 3.31B, D) and the superior and inferior ulnar collateral arteries (Figs. 3.32 and 3.23). Two sets of veins of the arm, superficial and deep, anastomose freely with each other. The two main superficial veins of the arm, the cephalic and basilic veins, are described earlier (see Figs. 3.11 and 3.28A). Paired deep veins, collectively constituting the brachial vein, accompany the brachial artery (see Fig. 3.12). The brachial vein begins at the elbow by union of the accompanying veins of the ulnar and radial arteries and ends by merging with the basilic vein to form the axillary vein. Both superficial and deep veins have valves.  Describe the arteries,veins,and nerves of the arm. Figure 3.33 Cubitalfossa.A. Superficialdissection.B. Deep dissection. The median nerve in the arm is formed in the axilla by the union of medial and lateral roots from the medial and lateral cords of the brachial plexus, respectively (see Fig. 3.28A, C). The nerve runs distally in the arm then descends into the cubital fossa, where it lies deep to the bicipital aponeurosis and median cubital vein. The median and ulnar nerves supply no branches to the arm; however, they supply articular branches to the elbow joint. The ulnar nerve in the arm arises from the medial cord of the brachial plexus, conveying fibers mainly from the C8 and T1 nerves (see Fig. 3.28C). It passes distally, on the medial side of the brachial artery then passes posterior to the medial epicondyle of the humerus to enter the forearm (Figs. 3.32 and 3.33). The musculocutaneous nerve arises from the lateral cord of the brachial plexus, pierces the coracobrachialis, and then continues distally between the brachialis and the biceps (see Fig. 3.28A, C). After supplying all three muscles of the anterior compartment of the arm, the nerve emerges lateral to the biceps brachii as the lateral cutaneous nerve of the forearm (Fig. 3.29). The radial nerve descends inferolaterally with the profunda brachii artery and curves around the humeral shaft in the radial groove. In the cubital fossa, it divides into deep and superficial branches (Fig. 3.33B). The radial nerve supplies the muscles in the posterior compartments of the arm and forearm and the overlying skin.  Describe the arteries,veins,and nerves of the arm. Figure B3.9 W rist-drop. Injury to the musculocutaneous nerve in the axilla is usually inflicted by a weapon such as a knife. A musculocutaneous nerve injury results in paralysis of the coracobrachialis, biceps, and brachialis; consequently, flexion of the elbow and supination of the forearm are greatly weakened. Loss of sensation may occur on the lateral surface of the forearm supplied by the lateral cutaneous nerve of the forearm. Injury to the radial nerve superior to the origin of its branches to the triceps brachii results in paralysis of the triceps, brachioradialis, supinator, and extensor muscles of the wrist and fingers. Loss of sensation occurs in areas of skin supplied by this nerve. When the radial nerve is injured in the radial groove, the triceps is usually not completely paralyzed but only weakened because only the medial head is affected; however, the muscles in the posterior compartment of the forearm that are supplied by more distal branches of the radial nerve are paralyzed. The characteristic clinical sign of radial nerve injury is wrist‐drop (inability to extend the wrist and fingers at the metacarpophalangeal joints). Instead, the wrist remains in the flexed position because of unopposed tonus of the flexor muscles and gravity.  Describe the arteries,veins,and nerves of the arm. Figure SA3.3 Surface anatom y of arm and cubitalfossa. The cubital fossa is the shallow triangular depression on the anterior surface of the elbow (Fig. 3.33A). The contents of the cubital fossa include the following (Fig. 3.33B): Terminal part of the brachial artery and the commencement of its terminal branches, the radial and ulnar arteries; the brachial artery lies between the biceps tendon and the median nerve. (Deep) accompanying veins of the arteries Biceps brachii tendon Median nerve Radial nerve, dividing into superficial and deep branches In the subcutaneous tissue overlying the cubital fossa are the median cubital vein, lying anterior to the brachial artery, and the medial and lateral cutaneous nerves of the forearm, related to the basilic and cephalic veins (Fig. 3.33A).  Describe the m uscles of the forearm in term s of their general Figure 3.34 attachm ents,innervations,and m ajor actions. Stepped transverse section (m id forearm ) dem onstrating com partm ents of forearm. The forearm is between the elbow and the wrist and contains two bones, the radius and the ulna, which are joined by an interosseous membrane (Fig. 3.34). The role of forearm movement, occurring at the elbow and radioulnar joints, is to assist the shoulder in the application of force and in controlling the placement of the hand in space. The tendons of the forearm muscles pass through the distal part of the forearm and continue into the wrist, hand, and fingers. The flexors and pronators of the forearm are in the anterior compartment and are innervated mainly by the median nerve; the one and a half muscles that are exceptions are innervated by the ulnar nerve (see Table 3.8). The median and ulnar nerves are terminal branches of the medial and lateral cords, each formed by anterior divisions of trunks. The extensors and supinators of the forearm are in the posterior compartment and are all innervated by the radial nerve. Functionally, the brachioradialis is a flexor of the elbow joint (Fig. 3.37A; see Table 3.9), but it is located in the extensor (posterior) compartment and is thus supplied by the radial nerve.  Describe the m uscles of the forearm in term s of their general Figure 3.35 attachm ents,innervations,and m ajor actions. M uscles of anterior com partm ent of forearm. A.Firstlayer.B.Second layer.C.Third layer.D. Fourth layer.1,wristjoint; 2,carpom etacarpaljoint;3, m etacarpophalangeal joint;4,proxim al interphalangealjoint;5, distalinterphalangeal joint. The flexor–pronator muscles are in the anterior compartment of the forearm (Figs. 3.34 and 3.35). The tendons of most flexor muscles pass across the anterior surface of the wrist and are held in place by the palmar carpal ligament (see Fig. 3.10) and the flexor retinaculum (transverse carpal ligament), thickenings of the antebrachial fascia. The flexor muscles are arranged in three layers or groups (Fig. 3.35): A superficial (first) layer or group of four muscles: pronator teres, flexor carpi radialis (FCR), palmaris longus, and flexor carpi ulnaris (FCU). These muscles are all attached proximally by a common flexor tendon to the medial epicondyle of the humerus, the common flexor origin. An intermediate (second) layer or group, consisting of one muscle: flexor digitorum superficialis (FDS) A deep (third) layer or group of three muscles: flexor digitorum profundus (FDP), flexor pollicis longus (FPL), and pronator quadratus  Describe the m uscles of the forearm in term s of their general Figure 3.36 attachm ents,innervations,and m ajor actions. Features of bones and attachm ents of m uscles of anterior com partm ent of forearm. The five superficial and intermediate muscles cross the elbow joint; the three deep muscles do not. The long flexors of the digits (FDS and FDP) also flex the metacarpophalangeal and wrist joints. The pronator quadratus is the prime mover for pronation.  Describe the m uscles of the forearm in term s of their general Table 3.8 attachm ents,innervations,and m ajor actions. M uscles of Anterior Com partm ent of Forearm  Describe the m uscles of the forearm in term s of their general Table 3.8(continued) attachm ents,innervations,and m ajor actions. M uscles of Anterior Com partm ent of Forearm  Describe the m uscles of the forearm in term s of their general Figure 3.37 attachm ents,innervations,and m ajor actions. M uscles and neurovascular structures of posterior com partm ent of forearm. A.Superficialdissection.B. Deep dissection. The extensor muscles are in the posterior (extensor–supinator) compartment of the forearm (Figs. 3.34 and 3.37), and all are innervated by branches of the radial nerve (see Fig. 3.17). These muscles may be organized into three functional groups: Muscles that extend and abduct or adduct the hand at the wrist joint: extensor carpi radialis longus (ECRL), extensor carpi radialis brevis (ECRB), and extensor carpi ulnaris (ECU) Muscles that extend the medial four digits: extensor digitorum, extensor indicis, and extensor digiti minimi (EDM) Muscles that extend or abduct the thumb: abductor pollicis longus (APL), extensor pollicis brevis (EPB), and extensor pollicis longus (EPL) The tendons of the APL and EPB bound the triangular anatomical snuff box laterally, and the tendon of the EPL bounds it medially (Fig. 3.37B). The snuff box (see dotted line in image above) is visible as a hollow on the lateral aspect of the wrist when the thumb is extended fully; this draws the APL, EPB, and EPL tendons up and produces a concavity between them. Observe that the: radial artery lies on the floor of the snuff box. radial styloid process can be palpated proximally, and the base of the 1st metacarpal can be palpated distally in the snuff box. scaphoid and trapezium can be felt in the floor of the snuff box between the radial styloid process and the 1st metacarpal.  Describe the m uscles of the forearm in term s of their general Table 3.9 attachm ents,innervations,and m ajor actions. M uscles of Posterior Com partm ent of Forearm  Describe the m uscles of the forearm in term s of their general Table 3.9(continued) attachm ents,innervations,and m ajor actions. M uscles of Posterior Com partm ent of Forearm  Describe the m uscles of the forearm in term s of their general Figure 3.38 attachm ents,innervations,and m ajor actions. Synovialsheaths of extensor tendons on distalforearm and dorsum of hand.A. Illustration with color- coded synovialsheaths.B. Transverse section through distalend of radius and ulna to show extensor tendons in their synovialsheaths. The extensor tendons are held in place in the wrist region by the extensor retinaculum, which prevents bowstringing of the tendons when the hand is extended at the wrist joint. As the tendons pass over the dorsum of the wrist, they are covered with synovial tendon sheaths, which reduce friction for the extensor tendons as they traverse the osseofibrous tunnels formed by the attachment of the extensor retinaculum to the distal radius and ulna (Fig. 3.38).  Describe the m uscles of the forearm in term s of their general Figure 3.39 attachm ents,innervations,and m ajor actions. Extensor m uscles of forearm. The extensor muscles are organized anatomically into superficial and deep layers. Four superficial extensors (ECRB, extensor digitorum, EDM, and ECU) are attached proximally by a common extensor tendon to the lateral epicondyle (Figs. 3.37A and 3.39; Table 3.9). The proximal attachment of the other two superficial extensors (brachioradialis and ECRL) is to the lateral supra‐ epicondylar ridge of the humerus.  Describe the arteries,veins,and nerves of the forearm. Figure 3.41 M uscles,vessels,and nerves of anterior aspect of forearm. The major nerves of the forearm are the median, ulnar, and radial (Figs. 3.41 and 3.42). Although the radial nerve appears in the cubital region, it soon enters the posterior compartment of the forearm. Besides the cutaneous branches, there are only two nerves of the anterior aspect of the forearm: the median and ulnar nerves.  Describe the arteries,veins,and nerves of the forearm. Figure 3.42 Nerves of forearm.A–C. M otor innervation.D. Cutaneous innervation. The median nerve is the principal nerve of the anterior compartment of the forearm. It enters the forearm with the brachial artery and lies medial to it and leaves the cubital fossa by passing between the heads of the pronator teres, giving branches to them, and then passes deep to the FDS, continuing distally through the middle of the forearm, between the FDS and the FDP (Fig. 3.41). The anterior interosseous nerve is its major branch. The ulnar nerve passes posterior to the medial epicondyle of the humerus. The ulnar nerve becomes superficial at the wrist, running on the medial side of the ulnar artery and the lateral side of the FCU tendon. The ulnar passes superficial to the flexor retinaculum to enter the hand, where it supplies the skin on the medial side of the hand. The radial nerve leaves the posterior compartment of the arm to cross the anterior aspect of the lateral epicondyle of the humerus. In the cubital region, the radial nerve divides into deep and superficial branches (see Fig. 3.33B). The deep branch of radial nerve arises anterior to the lateral epicondyle and pierces the supinator then winds around the lateral aspect of the neck of the radius and enters the posterior (extensor–pronator) compartment of the forearm, where it continues as the posterior interosseous nerve (Fig. 3.42C). The superficial branch of the radial nerve is a cutaneous and articular nerve that descends in the forearm under cover of the brachioradialis (Fig. 3.41). The superficial branch of the radial nerve (sensory or cutaneous) emerges in the distal part of the forearm and crosses the roof of the anatomical snuff box. It is distributed to skin on the dorsum of the hand (Fig. 3.42D).  Describe the arteries,veins,and nerves of the forearm. Figure 3.43 Arteries of forearm and hand.A.Overview.B. Distalforearm and hand. The brachial artery ends in the distal part of the cubital fossa opposite the neck of the radius by dividing into the ulnar and radial arteries, the main arteries of the forearm (Fig. 3.41). The ulnar artery descends through the anterior (flexor–pronator) compartment of the forearm, deep to the pronator teres and ultimately to the hand. Pulsations of the ulnar artery can be palpated on the lateral side of the FCU tendon, where it lies anterior to the ulnar head (Fig. 3.41). The ulnar nerve is on the medial side of the ulnar artery. The radial artery leaves the forearm by winding around the lateral aspect of the wrist and crossing the floor of the anatomical snuff box to reach the hand (Figs. 3.37 and 3.43). The pulsation of the radial artery is usually measured on the distal radius between the tendons of FCR and APL (Fig. 3.41). There are superficial and deep veins in the forearm, the superficial veins ascend in the subcutaneous tissue; deep veins accompany the deep arteries (e.g., radial and ulnar).  Describe the m uscles of the hand in term s of their general Figure 3.44 attachm ents,innervations,and m ajor actions. Palm ar fascia and fibrous digitalsheaths.A. Overview.B.Transverse section of4th digitatlevel ofproxim alphalanx. The palmar aspect of the hand features a central concavity that separates two eminences: a lateral more prominent thenar eminence at the base of the thumb and a medial, smaller hypothenar eminence proximal to the base of the 5th finger (Fig. 3.44A). The fascia of the palm is thin over the thenar and hypothenar eminences, but it is thick centrally where it forms the fibrous palmar aponeurosis and in the fingers where it forms the digital sheaths (Fig. 3.44). The palmar aponeurosis, a strong, well‐defined part of the deep fascia of the palm, covers the soft tissues and overlies the long flexor tendons. The proximal end or apex of the triangular palmar aponeurosis is continuous with the flexor retinaculum and the palmaris longus tendon. Distal to the apex, the palmar aponeurosis forms four longitudinal digital bands that radiate from the apex and attach distally to the bases of the proximal phalanges, where they become continuous with the fibrous digital sheaths (Fig. 3.44). The fibrous digital sheaths are ligamentous tubes that enclose the flexor tendon(s) and the synovial sheaths that surround them as they pass along the palmar aspect of their respective digit.  Describe the m uscles of the hand in term s of their general Figure 3.45 attachm ents,innervations,and m ajor actions. Com partm ents and spaces of hand.A. Transverse section showing com partm ents and spaces.B.Thenar and m idpalm ar spaces. A medial fibrous septum extends deeply from the medial border of the palmar aponeurosis to the 5th metacarpal. Medial to this septum is the medial or hypothenar compartment containing the hypothenar muscles (Fig. 3.45A). Similarly, a lateral fibrous septum extends deeply from the lateral border of the palmar aponeurosis to the 3rd metacarpal. Lateral to the septum is the lateral or thenar compartment containing the thenar muscles. Between the hypothenar and the thenar compartments is the central compartment containing the flexor tendons and their sheaths, the lumbrical muscles, the superficial palmar arterial arch, and the digital vessels and nerves (Fig. 3.45A). The deepest muscular plane of the palm is the adductor compartment containing the adductor pollicis. Between the flexor tendons and the fascia covering the deep palmar muscles are two potential spaces: the thenar space and the midpalmar space (Fig. 3.45). The midpalmar space is continuous with the anterior compartment of the forearm via the carpal tunnel.