Skeletal System II HAPP111 PDF

▪ The entire framework of bones and their cartilages, along with ligaments and tendons constitute the skeletal system. The study of bone structure and treatment of bone disorders is called osteology. ▪ Functions: 1. It supports surrounding structures 2. It protects vital visceral organs...

▪ The entire framework of bones and their cartilages, along with ligaments and tendons constitute the skeletal system. The study of bone structure and treatment of bone disorders is called osteology. ▪ Functions: 1. It supports surrounding structures 2. It protects vital visceral organs 3. It provides attachment to the muscles and creates leverage so assisting in body movements  4. It produces blood cells (hematopoiesis, hemopoiesis). This occurs in the red bone marrow. 5. For storage of mineral salts especially calcium and phosphorus to supply body needs (mineral homeostasis). Also, fat (triglycerides) in the form of yellow bone marrow. ▪ Classification of Bones ▪ According to shape 1. Long bones are considerably longer than they are wide. A long bone has a shaft (diaphysis) plus two ends (epiphyses). All limb bones except patella (kneecap) and the wrist and ankle bones are long bones. 2. Short bones are roughly cube-shaped. The bones of the wrist and ankles are examples. Sesamoid bones are special type of short bone that form in a tendon (example, the patella). 3. Flat bones are thin, flattened, and usually a bit curved. The sternum  breastbone) scapulae (shoulder blades), ribs, and most skull bones are flat bones) 4. Irregular bones have complicated shapes that fit none of the preceding classes. Examples include the vertebrae and the hip bones. ▪ Because they contain different types of tissue, bones are organs. Although bone (osseous) tissue dominates bones, they also contain nervous tissue. In their nerves, cartilage in their articular cartilages, dense connective tissue covering their external surface and muscle and epithelial tissues in their blood vessels. ▪ Bone structure at three levels: Gross, Microscopic, and Chemical ▪ Gross Anatomy ▪ Types of Bones. Every bone has a dense outer layer that looks smooth and solid, this external layer is known as compact (cortical) bone.  Internal to this is spongy (trabecular, cancellous) bone, a honeycomb of small needle-like or flat pieces called trabeculae (diploe for flat bones). In living bones, the open spaces between trabeculae are filled with red or yellow bone marrow. ▪ Bone structure at three levels: Gross, Microscopic, and Chemical ▪ Gross Anatomy ▪ Structure of a typical long bone. With few exceptions, all long bones have the same general structure: ▪ Diaphysis is the shaft that forms the long axis of the bone, constructed from collar of compact bone that surrounds central medullary cavity (red or yellow bone marrow) ▪ Epiphysis is the bone ends, broader than the diaphysis ▪ Metaphysis is the flared portion of the bone where the diaphysis and epiphysis meet (epiphysial line, a remnant of epiphyseal plate, a disc of hyaline cartilage that grows during childhood to lengthen the bone) ▪ The external surfaces of bones display projections, and openings (bone markings) serve as sites of muscle, ligament, and tendon  attachment, also conduits for blood vessels and nerves. Projections, or bone markings that bulge outward from the surface include heads, trochanters, spines and others. While bone markings that are depressions and openings include fossae (fossa), sinuses, foramina (foramen), and grooves, usually allowing nerves and blood vessels to pass. ▪ Bone structure at three levels: Gross, Microscopic, and Chemical ▪ Gross Anatomy ▪ Structure of a typical long bone. With few exceptions, all long bones have the same general structure: ▪ Membranes. The entire external surface of the bone except the joint surfaces is covered by a white, double-layered membrane called periosteum. Periosteum is richly supplied with nerve and blood vessels which pass through the shaft to enter the marrow cavity via nutrient foramen (openings). Perforating (Sharpey’s) fibers, tuft of collagen fibers extend from its fibrous layer into the bone matrix to secure periosteum to underlying bone.  ▪ Outer fibrous layer of periosteum is dense irregular connective tissue ▪ Inner osteogenic layer of periosteum, next to the bone surface, consists primarily of primitive stem cells (osteogenic cells) that give rise to all bone cells except bone-destroying cells ▪ A delicate connective tissue membrane called endosteum covers internal bone surfaces. The endosteum covers the trabeculae of spongy and lines the canals of compact bones. Like periosteum, endosteum contains osteogenic cells. ▪ Bone structure at three levels: Gross, Microscopic, and Chemical ▪ Microscopic Anatomy of Bone ▪ Five (5) major cell types populate bone tissue including osteogenic cells (osteoprogenitor), osteoblasts, osteocytes, bone lining cells, osteoclasts. All of these except osteoclasts originate from embryonic connective  tissue cells. ▪ Bone structure at three levels: Gross, Microscopic, and Chemical ▪ Microscopic Anatomy of Bone ▪ Although compact bone looks solid, a microscope reveals that it is riddled with passageways that serve as conduits for nerves and blood vessels. The structural unit of compact bone is called osteon (Haversian system). An osteon is a group of hollow matrix tube called lamella hence, compact bone also called lamellar bone. ▪ Running through the core of each osteon is the central canal, also called Haversian canal, containing small blood vessels and nerve fibers. Canals of second type called Volkmann’s (perforating) canals that connect the blood and nerve supply of medullary cavity to the central canals. Unlike central canals, perforating canals are not surrounded by concentric lamellae but like all internal bone cavities lined with endosteum. ▪ Spider-shaped osteocytes occupy lacunae at the junctions of the lamellae. Hairlike canals called canaliculi connect the lacunae to each other to the  central canal. ▪ Not all lamellae are part of complete osteon, incomplete (interstitial) lamellae either fill the gaps or remnants of osteons during bone remodeling. Circumferential lamellae, are lamellae that extend around the entire circumference of the diaphysis ▪ Bone structure at three levels: Gross, Microscopic, and Chemical ▪ Chemical composition of Bone ▪ Bone contains both organic and inorganic substances. ▪ Organic components include bone cells and osteoid (organic part of the matrix, composed of ground substance (proteoglycans and glycoproteins) and collagen). When organic and inorganic components are present in the right proportions, bone is extremely strong and durable without being brittle. Bone resilience is thought to come from sacrificial bonds in or between collagen molecules. These bonds stretch and break easily on impact. In the absence of continued trauma, sacrificial bonds  re-form ▪ Inorganic components consist of hydroxyapatites or mineral salts, largely calcium phosphates, as tiny, tightly packed, needle-like crystals in and around collagen fibers in the ECM. The crystals account for the exceptional hardness of the bones , which allow to resist compression. ▪ Classification of Bones ▪ According to development ▪ Ossification and osteogenesis are synonymous meaning the process of bone formation. ▪ In embryos this leads to the formation of the bony skeleton. ▪ Another form of ossification known as bone growth goes on until early adulthood as the body increases in size. Bones can grow thicker throughout life. ▪ However, ossification in adults serves mainly for bone remodeling and repair.  ▪ 1. In endochondral ossification, a bone develops by replacing hyaline cartilage, the resulting bone is known as endochondral bone. Except for clavicles, essentially all bones below the base of the skull form by endochondral ossification. ▪ 2. In intramembranous ossification, a bone develops from fibrous membrane and the bone is called a membrane bone. Intramembranous ossification forms the cranial bones of the skull (frontal, parietal, occipital, and temporal bones) and the clavicles. Mostly are flat bones. ▪ Hormonal regulation of Bone Growth ▪ The bone growth that occurs until young adulthood is exquisitely controlled by a symphony of hormones. During infancy and childhood, the single most important stimulus of epiphyseal plate activity is growth hormone released by the anterior pituitary gland. Thyroid hormones modulate the activity of growth hormone, ensuring that the skeleton has proper proportions as it grows. ▪ At puberty, sex hormones (testosterone in males and  estrogens in females) are released in increasing amounts. Initially it promotes growth spurt typical of adolescence, also masculinization and feminization of specific parts of the skeleton. Later the hormones induce epiphyseal plate closure, ending longitudinal bone growth. ▪ Excesses or deficits of any of these hormones can result in abnormal skeletal growth. For example, hypersecretion of growth hormone in children results in excessive height (giantism or gigantism) and deficits of growth hormone produce characteristic type of dwarfism. ▪ Hormonal regulation of calcium release (bone resorption) ▪ The hormonal controls primarily involve parathyroid hormone (PTH), produced by the parathyroid glands. To a much lesser extent calcitonin, produced by parafollicular cells  (C-cells) of thyroid gland. ▪ When the blood levels of calcium decline (hypocalcemia), PTH is released. The increased PTH level stimulates osteoclasts to resorb bone, releasing calcium. The opposite is true for high blood calcium (hypercalcemia). ▪ In humans, calcitonin appears to be a hormone in search of a function because its effects on calcium homeostasis are negligible. When administered at pharmacological (abnormally high) doses, it does lower blood calcium levels temporarily. ▪ These hormonal controls act to preserve blood calcium homeostasis, not the skeleton’s strength. ▪ Bone disorders ▪ Imbalances between bone deposit and bone resorption underlie nearly every disease that affects the human skeleton ▪ Osteomalacia (soft bones) in which the bones are poorly mineralized. Osteoid is produced,  but calcium salts are not adequately deposited, so bones are soft and weak. Osteomalacia (adult) and rickets (children) are caused by insufficient calcium in the diet or by a vitamin D deficiency. ▪ Osteoporosis refers to a group of diseases in which the bone resorption outpaces bone deposit. The composition of the matrix remains normal but bone mass declines, and the bones become porous and light. Even though osteoporosis affects the entire skeleton, the spongy bone of the spine and the neck of femur (broken hip) are the most susceptible to fracture in people with osteoporosis. ▪ Osteoporosis occurs most often in the aged, particularly in postmenopausal women, although men may also develop but to lesser extent. Sex hormones – androgens in males and estrogen s in females – help maintain the health and normal density of the skeleton by restraining osteoclasts and promoting deposit of new bone. After menopause, estrogen secretion wanes, and estrogen deficiency is strongly implicated in osteoporosis in older women. Osteoporosis can develop at any age because of immobility. It can also occur in males with prostate cancer who are being treated with androgen-suppressing drugs. ▪ Osteoporosis has traditionally been treated with calcium and vitamin D supplements, weight-bearing exercise and hormone (estrogen) replacement therapy (HRT). Bisphosphonates decrease osteoclast activity and number. The monoclonal drug, denosumab reduces fractures in men fighting prostate cancer and improves bone density in the elderly. ▪ Despite remarkable strength, bones are susceptible to fractures, or breaks. ▪ Fractures may be classified by:  1. Position of the bone ends after fracture ▪ In nondisplaced fractures, the bone ends retain their normal position. In displaced fractures, the bone ends are out of normal alignment 2. Completeness of the break ▪ If the bone is broken through, the fracture is complete fracture. If not, it is an incomplete fracture. 3. If bone ends penetrate skin ▪ If it penetrates the skin, it is open (compound) fracture. If not, it is closed (simple) fracture. ▪ In addition to these three (3) classification, all fractures can be described in terms of location of the fracture. Its external appearance, and or nature of the break. ▪ Treatment involves reduction, the realignment of the broken bone ends. In closed or external reduction, the physician’s hands coax the bone ends into position. In open or internal reduction, the bone ends are secured together surgically with pins or wires. After the broken bone is reduced, it is immobilized either by cast or traction to allow healing. ▪ The 206 named bones of the human skeleton are divided into two (2) groups: 1. Axial skeleton ▪ Consists of eighty (80) bones that protect, support and carry other body parts ▪ Skull ▪ Cranial bones (8) ▪ Facial bones (14) ▪ Ear ossicles (6) ▪ Hyoid bone (1) ▪ Vertebrae (cervical, thoracic, lumbar, sacral, coccyx) (26) ▪ Ribs (24) ▪ Sternum (1) 2. Appendicular skeleton ▪ Consists of 126 bones that help us move from place to place (locomotion) and manipulate our environment ▪ Bones of upper extremities (64 bones, including the shoulder girdle) ▪ Bones of lower extremities (62 bones,  including the pelvic girdle) ▪ The skull is the body’s most complex bony structure. It is formed by cranial and facial bones, 22 in all. The cranial bones or cranium, enclose and protect the fragile brain and furnish attachment sites for head and neck muscles. ▪ The cranium can be divided into a vault and a base ▪ The cranial vault also called calvaria forms the superior, lateral, and posterior aspects of the skull, as well as forehead ▪ The cranial base forms the skull’s inferior aspect. Internally , prominent bony ridges divide the base into three (3) distinct fossae – the anterior, middle, and posterior cranial fossae ▪ The brain is said to occupy the cranial cavity ▪ The eight (8) cranial bones are the paired parietal and temporal bones and the unpaired frontal, occipital, sphenoid, and ethmoid bones. ▪ A. Cranial Bones (8 bones) Frontal bone (1) ▪ The shell-shaped frontal bone forms the anterior cranium. It articulates posteriorly with the paired parietal bones via the prominent coronal suture. The most anterior part of the frontal lobe is the vertical squamous part (forehead) that ends inferiorly at the supraorbital margins, the thickened superior margins of the orbits. Each supraorbital margin is pierced by supraorbital foramen (notch) that allows supraorbital artery and nerve to pass the forehead. The smooth portion of the frontal bone between orbits is the glabella. The areas lateral to the glabella contain sinuses, called frontal sinuses. Occipital bone (1) ▪ The occipital bone forms most of the skull’s posterior wall and base. It articulates with the paired parietal and temporal bones via lambdoid and occipitomastoid sutures. In the base of the occipital bone is the foramen magnum (large hole) through which the inferior part of the brain connects with the spinal cord. The foramen magnum is flanked laterally by two (2) occipital condyles that articulate with the first  vertebra of the spinal column that permits nodding (yes) motion of the head. Hidden superiorly to each occipital condyle is a hypoglossal canal, through which cranial nerve (XII) passes. Just superior to the foramen magnum is a median protrusion called external occipital protuberance, a knoblike projection just below the most bulging part of your posterior skull. ▪ A. Cranial Bones (8 bones) Sphenoid bone (1) ▪ The bat-shaped sphenoid bone is considered the keystone of the cranium because it forms central wedge that articulates with all other cranial bones. It consists of a central body and three (3) pairs of processes: The greater wings (lateral to sphenoid body), lesser wings (floor of the anterior cranial fossa), and pterygoid processes (inferior from the junction of body and greater surface of the body (hypophyseal wings). The superior fossa) bears a saddle shaped prominence, the sella turcica (Turk’s saddle) forms a snug enclosure for pituitary gland. The optic canals lie anterior to the sella  turcica, allow the optic nerves (cranial nerve II) to pass to the eyes. Ethmoid bone (1) ▪ Lying between the sphenoid and the nasal bone of the face, it is the most deeply situated bone of the skull. It forms most of the bony area between the nasal cavity and the orbits. The superior surface of the ethmoid is formed by the paired horizontal cribiform plates which help form the roof of the nasal cavity and the floor of anterior cranial fossal. The crifibiform plates are punctured by tiny holes called cribiform foramina that allows olfactory nerves to pass through. Projecting superiorly between cribiform plates is a triangular process called crista galli that helps secure brain in the cranial cavity. ▪ A. Cranial Bones (8 bones) Parietal bones (2) ▪ Two large parietal bones are curved and rectangular bones that form most of the superior and lateral aspects of the skull.  Coronal suture (parietal and frontal meets anteriorly), Sagittal suture (parietal bones meet superiorly at the cranial midline), Lambdoid suture (parietal bones meet the occipital bone posteriorly), and Squamous suture (where parietal and temporal bone on the lateral aspect of the skull, one on each side) Temporal bones (2) ▪ The two (2) temporal bones lie inferior to the parietal bones and meet them at the squamous sutures. The temporal bones form the inferolateral aspects of the skull and parts of the cranial base. Each temporal bone has three (3) parts: The flaring squamous part ends at the squamous suture; The tympanic part of the temporal bone surrounds the external ear canal (external acoustic meatus);The thick petrous part of the temporal bone houses the middle and internal ear cavities which contain sensory receptors for  hearing and balance. A conspicuous feature of the petrous part is the mastoid process which acts as am anchoring site for some neck muscles. ▪ Facial Bones ▪ Mandible ▪ The u-shaped mandible or lower jawbone, is the largest, strongest bone of the face. It has a body, which forms the chin, and two (2) upright rami. The anterior coronoid process is an insertion point for the large temporalis muscle that elevates the lower jaw during chewing. The posterior condylar process articulates with mandibular fossa of temporal bone forming the temporomandibular joint (TMJ). The mandibular body anchors the lower teeth. Its superior border called alveolar process contains the sockets (dental alveoli) in which the teeth are  embedded. The mandibular foramina, one on the medial surface of each ramus, permit the nerves responsible for tooth sensation. ▪ Vomer ▪ The slender, plow-shaped vomer lies in the nasal cavity, where it forms part of the nasal septum. ▪ Facial Bones ▪ Maxillary ▪ Maxillary bones or maxillae are fused medially. They form the upper jaw and the central portion of the facial skeleton. All facial bones except mandible articulate with the maxillae hence, considered the keystone bones of the facial skeleton. The maxillae carry the upper teeth in their alveolar processes. ▪ Nasal ▪ The thin, rectangular nasal bones are fused medially, forming the bridge of the nose. They articulate with the frontal bone superiorly, the maxillary bones laterally, and the perpendicular plate of the ethmoid bone posteriorly. ▪ Facial Bones ▪ Zygomatic, also called malar. The irregularly shaped zygomatic bones commonly called cheekbones, form the prominences of the cheeks and part of the inferolateral margins of the orbits. They articulate with the zygomatic processes of the temporal bones posteriorly, with  zygomatic processes of the frontal bone superiorly and with the zygomatic processes of the maxillae anteriorly. ▪ Lacrimal is a fingernail-shaped bones that contribute to the medial walls of each orbit. They articulate with the frontal bone superiorly, the ethmoid bone posteriorly, and the maxillae anteriorly. Each lacrimal bone contains a deep groove that helps form a lacrimal fossa, that houses lacrimal sac, passageway that allows tears to drain from the eye surface into the nasal cavity. ▪ Facial Bones ▪Palatine is an L-shaped bone  fashioned from two bony plates, horizontal and perpendicular and has three (3)important articular processes, the pyramidal, sphenoidal, and orbital. ▪ Inferior nasal conchae (inferior turbinates). The paired inferior nasal conchae are thin, curved bones that project medially from the lateral walls of the nasal cavity, just inferior to the middle nasal  conchae of the ethmoid bone. ▪ Auditory Ossicles ▪ Malleus (Hammer, 2) ▪ Incus (Anvil, 2) ▪ Stapes (Stirrup, 2) ▪ Small bones in middle ear in temporal bone ▪ Hyoid bone. The hyoid bone is a horseshoe shaped bone that lies in the anterior neck just inferior to the mandible and looks like a miniature version of it. The hyoid bone is unique in that it is the only bone of the body that does not articulate directly with other bone. It has a body and two (2) horns or cornua (greater, lesser), the hyoid bone acts as a movable  base for the tongue. ▪ Vertebral column also called the spine or spinal column. The vertebral column consists of 26 irregular bones connected in such a way that a flexible, curved structure results. ▪ The spine extends from the skull to the pelvis, where it transmits the weight of the trunk to the lower limbs. It also surrounds and protects the delicate spinal cord and provide attachment points for the ribs and for the muscles of the back and neck. ▪ Individual vertebra is separated by intervertebral disc. Each intervertebral disc is composed of two parts, the inner gelatinous nucleus pulposus that gives elasticity and compressibility of the disc and outer anulus fibrosus, composed of collagen fibers, that limits expansion of nucleus pulposus. ▪ Exaggerations of the spinal curvature are Kyphosis (when the posterior curvature is accentuated in the thoracic area), Lordosis (when the  anterior curvature is accentuated in the lumbar area) and Scoliosis (when there is lateral curvature and rotation of the vertebrae) ▪ The first two cervical vertebrae, the atlas and the axis, are somewhat more robust than the typical cervical vertebra. They have no intervertebral disc between them. The atlas (C1) has no body and no spinous process. The axis, which has a body and the other typical vertebral processes, is not as specialized as the atlas. In fact, its only unusual feature is the knoblike dens projecting superiorly from its body. ▪ The triangular sacrum, which shapes the posterior wall of the pelvis, is formed by five fused vertebrae (S1–S5) in adults. The coccyx, our tailbone, is a small triangular bone that articulates superiorly with the sacrum The sternum (breastbone) lies in the anterior midline of the thorax. Sternum is a flat bone approximately 15 cm (6 inches) long, resulting from the fusion of three bones: the  manubrium, the body, and the xiphoid process. The sternum has three important anatomical landmarks: the jugular notch, the sternal angle, and the xiphisternal joint. The easily palpated jugular (suprasternal) notch is the central indentation in the superior border of the manubrium. The sternal angle is felt as a horizontal ridge across the front of the sternum, where the manubrium joins the sternal body. The xiphisternal joint is the point where the sternal body and xiphoid process fuse. It lies at the level of the ninth thoracic vertebra. Twelve pairs of ribs form the flaring sides of the thoracic cage. All ribs attach posteriorly to the thoracic vertebra and curve inferiorly toward the anterior body surface. The superior seven rib pairs  attach directly to the sternum by individual costal cartilages. These are true or vertebra sternal ribs. The remaining five pairs of ribs are called false ribs because they either attach indirectly to the sternum or entirely lack a sternal attachment. Rib pairs 8–10 attach to the sternum indirectly, each joining the costal cartilage immediately above it. These ribs are also called vertebra-chondral ribs. The inferior margin of the rib cage, or costal margin is formed by the costal cartilages of ribs 7–10. Rib pairs 11 and 12 are called vertebral ribs or floating ribs because they have no anterior attachments. Instead, their costal cartilages lie embedded in the muscles of the lateral body wall. ▪ Bones of the limbs and their girdles are collectively called the appendicular skeleton because they are  appended to the axial skeleton. The pectoral girdles attach the upper limbs to the body trunk. The more study pelvic girdle secures the lower limbs. ▪ The pectoral or shoulder girdle consists of the clavicle anteriorly and the scapula posteriorly. The paired pectoral girdles and their associated muscles form your shoulders. 1. The clavicles or collarbones are s-shaped bones that can be felt along their entire course as they extend horizontally across the superior thorax. Besides anchoring many muscles, the clavicles act as braces. This bracing function becomes obvious when a clavicle is fractured. The entire shoulder region collapses medially. Each clavicle is cone shaped at its medial sternal end, which attached to the sternal manubrium, and flattened at its lateral acromial end which articulates with the scapula. The trapezoid line and the conoid tubercle for example are anchoring points for a ligament that connects the clavicle to the scapula. ▪ The pectoral or shoulder girdle consists of the clavicle anteriorly and the scapula posteriorly. The paired pectoral girdles and their associated muscles form your shoulders. 2. The scapulae, or shoulder blades are thin, triangular flat bones. The scapulae lie on the dorsal surface of the rib cage, between ribs 2 and 7. The anterior or costal surface of the scapula is relatively featureless. Its posterior surface bears a prominent spine that is easily felt. The ends laterally in an enlarged, roughened triangular projection called the acromion. Projecting anteriorly is the coracoid process which helps anchor the biceps muscle of the arm. It is bounded by the suprascapular notch (a nerve passage) medially and by the glenoid cavity laterally, shallow fossa that articulates with the humerus of the arm. Several large fossae appear on both sides of the scapula, the infraspinous and supraspinous are inferior and superior respectively to the spine. The subscapular  fossa is the shallow concavity formed by the entire anterior scapular surface. ▪ Humerus ▪ The humerus the sole bone of the arm, is a typical long bone. It articulates with the scapula at the shoulder and with the radius and ulna (forearm bones) at the elbow. ▪ At the proximal end of the humerus is its smooth hemispherical head which fits into the glenoid cavity of the scapula. Immediately inferior to the head is a slight constriction, the anatomical neck. Just inferior to this are the lateral greater tubercle and the more medial lesser tubercle separated by the intertubercular sulcus, or bicipital groove. Just distal to the tubercles is the surgical neck, most frequently fractured part of the humerus. About midway the shaft on its lateral side is the deltoid tuberosity, attachment site for the deltoid muscle of the shoulder. ▪ At the distal end of the humerus are two (2) condyles, a medial trochlea and the lateral ball-like capitulum. These condyles articulate  with the ulna and the radius. ▪ Superior to the trochlea on the anterior surface is coronoid fossa. On the posterior surface is the deeper olecranon fossa. These two (2) depressions allow the corresponding processes of the ulna to move freely when extended. A small radial fossa, lateral to the coronoid fossa, receives the head of the radius when the elbow is flexed. ▪ Two parallel long bones, the radius and the ulna, form the skeleton of the forearm or antebrachium. Their proximal ends articulate with the humerus; their distal ends form joints with bones of the wrist. The radius and ulna are connected along their entire length by a flat ligament, the interosseous membrane. In the anatomical position, the radius lies laterally (on thumb side) and the ulna medially. 1. The ulna is slightly longer than the radius. It bears two (2) prominent processes, the olecranon (elbow) and the coronoid process, separated by a deep concavity, the trochlear notch. On the lateral side of the coronoid process isa small depression,  the radial notch, where the ulna articulates with the head of the radius. Distally the ulnar shaft narrows and ends in a head. Medial to the head is the ulnar styloid process, from which a ligament runs to the wrist 2. The radius is thin at its proximal end and wide distally. Just inferior to the head is the rough radial tuberosity which anchors the biceps muscle of the arm. Distally, where the radius is expanded, it has a medial ulnar notch which articulates with the ulna, and a lateral radial styloid process. ▪ The skeleton of the hand includes the bones of the carpus (wrist); the bones of the metacarpus (palm); and the phalanges (bones of the fingers). 1. The carpus consists of eight (8) marble size short bones or carpals united by ligaments. Sally left the party to take Cindy home. 2. Five (5) metacarpus are small long bones not named but instead are  numbered I to V from thumb to little finger. 3. The fingers or digits of the upper limb are numbered I to V beginning with the thumb or pollex. In most people, the third finger is the longest. Each hand contains 14 miniature long bones called phalanges. Except for the thumb, each finger has three (3) phalanges: distal, middle, and proximal. The thumb has no middle phalanx. ▪ The pelvic girdle, or hip girdle is formed by the sacrum and a pair of hip bones (os coxae, coxal bone). Each hip bone unites with its partner anteriorly and with the sacrum posteriorly. ▪ Irregularly shaped hip bones consists of three (3) separate bones during childhood: the ilium, ischium, and pubis. In adults, these bones are firmly fused and their boundaries are indistinguishable. At the point of fusion of these 3 bones, is a deep hemispherical socket called acetabulum which receives the head of the femur. 1. The ilium is a large flaring bone that forms the superior region of a hip bone. It consists of a body and a superior winglike portion called ala. 2. The ischium forms the posteroinferior part of the hip bone. It has a thicker superior body adjoining the ilium and a thinner, inferior ramus. 3. The pubis or pubic bone forms the anterior portion of the hip bone. In the anatomical position, it lies nearly horizontally and the urinary bladder rests upon it. ▪ The femur, the single bone of the thigh, is the largest, longest, strongest bone in the body ▪ Proximally the femur articulates with the  hip bone and then courses medially as it descends toward the knee. The ball-like head of the femur has a small central pit called the fovea capitis. The neck is the weakest part of the femur and is often fractured, an injury commonly called a broken hip. ▪ At the junction of the shaft and neck are the lateral greater trochanter and posteromedial lesser trochanter. These projections serve as sites of attachment for thigh and buttock muscles. The two (2) trochanters are connected by the intertrochanteric line anteriorly and by the prominent intertrochanteric crest posteriorly. ▪ The patella is a triangular sesamoid bone enclosed in the tendon (quadriceps) that secures the anterior thigh muscles to the tibia. ▪ Two parallel bones, tibia and fibula, form the skeleton of the leg. These two (2) bones are connected by an interosseous membrane and articulate with each other both proximally and distally. 1. The tibia (shinbone) receives the weight of the body from femur and transmits it to the foot. It is the second only to the femur in size and strength. 2. The fibula is a sticklike bone with slightly expanded ends. It articulates proximally and distally with lateral aspects of the tibia. Its proximal end is its head; its distal end is the lateral malleolus. ▪ The skeleton of the foot includes the bones of the tarsus, the bones of the metatarsus, and the phalanges, or toe bones. 1. The tarsus is made up of seven (7) bones called tarsals that form the posterior half of the foot. The Cab in New Mexico Is Land Cruiser. 2. The metatarsus consists of five (5) small, long bones called metatarsals. These are numbered I to V beginning on the medial (great toe) side of the foot. 3. The 14 phalanges of the toes are a good deal smaller than those of the fingers. There are three phalanges in each digit except for the great toe, the hallux. The hallux has only two, proximal and distal.