Handout Skeletal System PDF

11/18/2024  gives the vertebrate body shape Skeletal...

11/18/2024  gives the vertebrate body shape Skeletal Skeletal  supports its weight  offers a system of levers that together with muscles System System produces movement  protects soft parts such as nerves, blood vessels, and other viscera 2 Skeletal System  Cranial Skeleton/Skull EXOSKELETON ENDOSKELETON Postcranial Skeleton  Vertebral column  Limbs formed from or within the integument forms deep within the body from mesoderm and other sources, not Endoskeleton  Girdles  Associated structures (Ribs the dermis giving rise to bone and directly from the integument and Shells) the epidermis to keratin. Tissues contributing to the endoskeleton include fibrous connective tissue, bone, and cartilage 3 4  11/18/2024 Cranium actually a composite structure formed of three distinct parts Splanchnocranium (yellow) which first CRANIAL arose to support pharyngeal slits in protochordates Chondrocranium (blue) underlies and SKELETON supports the brain and is formed of endochondral bone or of cartilage, or both Dermatocranium (pink) a contribution that in later vertebrates forms most of the outer casing of the skull and is composed of dermal bones 5 6  collective term that refers to the fused cranial components immediately surrounding and used as an equivalent term for encasing the brain the chondrocranium along with Braincase  dermatocranium + chondrocranium + splanchnocranium Neurocranium fused or attached sensory capsules—the supportive nasal, optic, and otic capsules 7 8  11/18/2024 Chondrocranium  Neurocranium  Is the primitive cartilaginous skeletal structure of the fetal skull that grows to envelop the rapidly growing embryonic brain  Includes the box that encloses the brain and the capsules surrounding the sense organs  It protects the brain  The chondrocranium in different species can vary greatly, but in general it is made up of five components:  the sphenoids Chondrocranium  the mesethmoid  the occipitals /Neurocranium  the optic capsules  nasal capsules Chondrocranium Chondrocranium Embryology Cartilaginous fishes (elasmobranchs): the chondrocranium does not ossify. Instead the 1. Condensations of head mesenchyme form elongate cartilage grows still farther upward and over the brain to complete the protective walls and cartilages next to the notochord roof of the braincase and it is retain throughout life 2. Forms cartilage at 6 pairs of isolated regions the expanded and enveloping chondrocranium supports and protects the brain within Bony fishes, lungfishes, & most ganoids: retain highly cartilaginous neurocranium that is covered by membrane bone a. parachordal (posterior pair) Other bony vertebrates: embryonic cartilaginous neurocranium is largely replaced by b. polar (middle pair, only in some vertebrates) replacement bone (the process of endochondral ossification occurs almost simultaneously at c. trabeculae (anterior pair) several ossification centers) d. The occipital the chondrocranium is primarily an embryonic structure serving as a scaffold for the e. The otic, optic, and nasal capsules developing brain and as a support for the sensory capsules 11 12  11/18/2024 Chondrocranium Embryology Splanchnocranium 3. As development proceeds, these cartilages fuse.  The splanchnocranium is an ancient 4. The region between the nasal capsules chordate structure formed by the fusion of the anterior tips of  In vertebrates, the splanchnocranium the trabeculae is the ethmoid plate generally supports the gills and offers 5. The parachordals grow together across the midline to form the basal plate between attachment for the respiratory muscles the otic capsules. while some elements contribute to the 6. The occipitals grow upward and around jaws and hyoid apparatus the nerve cord to form the occipital arch Collectively, all of these expanded and fused cartilages constitute the chondrocranium 13 Splanchnocranium Embryology Splanchnocranium Embryology 1. The splanchnocranium arises from neural Branchial arches that support the mouth are called jaws crest cells The first fully functional arch of the jaw is the mandibular 2. The neural crest cells migrate into the walls arch, the largest and most anterior of the modified series of of the pharynx to form pharyngeal arches arches between the gills a. Palatoquadrate (Dorsal) - It contributes to the upper 3. Each arch can be composed of a series of jaw up to five articulated elements per side: b. Meckel’s cartilage (mandibular cartilage) (Ventral) - It 1. Pharyngobranchial contributes to the lower jaw 2. Epibranchial The second arch is called the hyoid arch, most prominent 3. Ceratobranchial component is the hyomandibula 4. Hypobranchial In mammals, the ventral portion is involved in support the 5. Basibranchial elements tongue, muscles used for swallowing and jaw movements Branchial arches I-V are associated with the gill apparatus. Pharyngeal arches of aquatic vertebrates usually are associated with In mammals they eventually contribute to the larynx their respiratory gill system, they are referred to as branchial arches, or gill arches 15 16  11/18/2024 Dermatocranium Dermatocranium Parts of the Dermatocranium The dermatocranium is the dermal bone that is believed to be derived from the external 1.Facial series: Premaxilla, Maxilla, Nasals armor of primitive fish 2.Orbital series: Lacrimal, Prefrontal, Postfrontal, Postorbital, Jugal  Phylogenetically, these bones arise from the bony armor of the integument of early fishes and sink inward to become applied to the chondrocranium and splanchnocranium 3.Temporal series: Intertemporal, Supratemporal, Tabular, Squamosal, Quadratojugal  Bony elements of the armor also become associated with the endochondral elements of the pectoral girdle to give rise to the dermal components of this girdle 4.Vault series: Frontal, Parietal, Postparietal 5.Palatal series: Vomer, Palatine, Ectopterygoid, Pterygoid,  The dermatocranium forms the sides and roof of the skull to complete the protective bony Parasphenoid case around the brain; it forms most of the bony lining of the roof of the mouth, and encases much of the splanchnocranium 6.Mandibular series: Lateral bones: dentary, splenials, angular, surangular. Medial bones: prearticular,  Teeth that arise within the mouth usually rest on dermal bones coronoids 18 Dermal Bone Series Dermal Bone Series 3. Temporal series (green) lies behind the orbit, completing 1. Facial Series (pink) encircles the external naris and the posterior wall of the braincase collectively forms the snout a) intertemporal, supratemporal, and tabular makes up a) maxilla and premaxilla define the margins of the the medial part of the temporal series snout and usually bear teeth b) Squamosal and quadratojugal complete the b) nasal lies medial to the naris temporal series and form the “cheek” 2. Orbital series (light-blue) The dermal bones encircle the eye to define the orbit superficially 4. Vault Series (yellow) the vault, or Roofing bones, runs across the top of the skull and covers the brain beneath a) lacrimal takes its name from the nasolacrimal (tear) duct 3. Frontal b) prefrontal, postfrontal, and postorbital continue 4. Postparietal the ring of bones above and behind the orbit. 5. Parietal occupying the center of the roof and c) jugal usually completes the lower rim of the orbit defining the small parietal foramen if it is present 19 20  11/18/2024 Dermal Bone Series 5. Palatal Series (orange) The dermal bones of the primary palate cover much of the roof of the mouth a. pterygoid - The largest and most medial b. vomer, palatine, ectopterygoid - Teeth may be present Overview of the on any or all four palatal bones c. parasphenoid 6. Mandibular series (violet) a. dentary - tooth-bearing b. splenials, angular (posterior corner of the mandible) Skull Morphology and the surangular (above) c. Many of these bones wrap around the medial side of the mandible and meet the prearticular and one or several coronoids to complete the medial mandibular wall Left and right mandibles usually meet anteriorly at the midline in a mandibular symphysis 21 22 Braincase Braincase The occipital bones form the end of this Braincase or neurocranium, the upper and sphenoid platform. back part of the skull, which forms a These occipital bones are made up protective case around the brain. Basioccipital Supraoccipital Sharks: the braincase is an elaborate and paired exoccipitals Close the posterior wall of the braincase cartilaginous case around the brain except for a large hole they define, the Fish and tetrapods: the braincase is foramen magnum, through which the extensively ossified spinal cord runs. Occipital condyle, a single or double Braincase as a box with a platform of surface produced primarily within the basioccipital, where articulation (is where endoskeletal elements supporting the two bones come together) of the skull with brain, all encased in exoskeletal bones the vertebral column 23 24  11/18/2024 Jaws Jaws Upper jaw a pair of bones that form the framework Sharks: The palatoquadrate is fully functional in the jaws of the mouth of vertebrate animals, Bony fishes and tetrapods: makes limited contributions to usually containing teeth and including a the skull through its two derivatives: Epipterygoid: which fuses to the neurocranium movable lower jaw and an upper jaw Quadrate: which suspends the lower jaw, except in mammals Jaws function by moving in opposition to The dermal maxilla and premaxilla replace the each other and are used for biting, palatoquadrate as the upper jaw chewing, and the handling of food 25 26 Jaws Hyoid The hyoid, or hyoid apparatus, is a ventral derivative of Lower jaw, or mandible the splanchnocranium behind the jaws bone which suspend the tongue and larynx Sharks: Meckel’s cartilage It consists of a main body, the corpus, and extensions, the cornua (“horns”) Most Fish and Tetrapods: Meckel’s Elements of the hyoid apparatus are derived from the cartilage persists but is enclosed in ventral parts of the hyoid arch and from parts of the first exoskeletal bone of the few branchial arches Larval amphibians: the branchial bars persist but form a dermatocranium, which also supports reduced hyoid apparatus that supports the floor of the teeth mouth and functional gills Mammals: the lower jaw consists of a Adult amphibians: the gills and the associated part of the hyoid apparatus are lost, although elements persist single bone, the dermal dentary within the floor of the mouth usually to support the The anterior tooth-bearing part of the tongue dentary is its ramus Fish: it supports the floor of the mouth Mammals: the distal end of the hyoid horn fuses with the Jaw-closing muscles are inserted on otic region of the braincase to form the styloid process the coronoid process, an upward 27 28 extension of the dentary  11/18/2024 Cranial Kinesis Cranial kinesis refers to movement within the skull we use cranial kinesis to mean movement between the Cranial upper jaw and the braincase about joints between them Kinetic skulls means having mobile joints between various parts of the skull, e.g., being able to unhinge the jaws Kinesis Found in ancient fishes, bony fishes (especially teleosts), very early tetrapods, most reptiles, birds, and early therapsid ancestors to mammals Akinetic skulls means no such movement between upper jaw and braincase present in modern amphibians, turtles, crocodiles, and mammals (except rabbits) 29 30 Cranial Kinesis Cranial Kinesis Advantages: Advantages for Akinetic skulls: Cranial kinesis provides a way to change the size and configuration of the mouth rapidly. Loss of kinesis in mammals In fishes and other vertebrates that feed in water, leaves them with an akinetic rapid kinesis creates a sudden reduction of pressure in the buccal cavity so that the animal can suck in a skull, which allows infants to surprised prey (Suction feeding) suckle easily Cranial kinesis also allows tooth bearing bones to move quickly into strategic positions during rapid feeding Juvenile and adult mammals In many venomous snakes, linked bones along the sides of can chew firmly with sets of the skull can rotate forward. specialized teeth that work The venomous viper erects the maxillary bone bearing the fang and swings it from a folded position accurately from a secure, along its upper lip to the front of the mouth, where it akinetic skull can more easily deliver venom into prey. 32 33  11/18/2024 Skull Function and Design Skull Skull Functions It protects and supports the brain and its sensory receptors It may house cooling equipment to cool the brain during sustained activity Function and or during a rise in environmental temperature In many active terrestrial mammals, the nasal epithelium lining the nasal Design passages dissipates excess heat by evaporation as air moves across this moist lining The skull of many animals also supports the voice box and occasionally serves as a sound resonator to deepen or amplify an animal’s call 34 35 Feeding in Water The higher viscosity of water presents both problems and opportunities for the animal feeding in water Problem: Feeding in water poses a disadvantage in that water easily carries shock or pressure waves (“bow waves”) immediately in front of the predator approaching its food Opportunity: Prey Capture On the other hand, when a vertebrate quickly gulps water into its mouth, the viscosity of the water drags along the prey as well – suction feeding 37  11/18/2024 Suspension Feeding Suspension Feeding 2 Suspension feeding is the capture and ingestion of food particles that are suspended in water Least common: Most suspension feeders are: a Sieve can be used to strain suspended benthic (bottom-dwelling) organisms particles larger than the pores of the 1 sieve herbivorous/detritus feeding style As the stream of water passes through the Mechanism: sieve, the particles are held back and then 1. Captured particles are usually smaller than the collected from the face of the selective filter pores of the filter. This method is rare among animals because 2. They may collide directly with the filter or the relatively large particles filtered tend to 3 because of their inertia, they deviate from the plug and foul the sieve Buccal Cirri streamlines to collide with the mucus-covered Example: Buccal Cirri (amphioxus) surface of the filter Gill rakers (fishes) 3. Upon impact, the particles cling to the sticky mucus and are rolled up in mucous cords, and When the filter is clogged = these fishes can clear the material by a then are passed by cilia into the digestive tract38 kind of cough or quick expansion of the gill arches 39 Suction Feeding Feeding in Air Suction feeding is a method of ingesting a prey item in fluids by sucking the prey into the Terrestrial feeding in most amphibians and predator's mouth many lizards requires a projectile tongue It is a highly coordinated behavior achieved by Lingual feeding - when an animal uses a oral the dorsal rotation of the dermatocranium, muscular organ, most notably the tongue lateral expansion of the suspensorium, and that's normally enlarged for foraging and the depression of the lower jaw and hyoid hunting and acts as a tool to obtain certain The buccal cavity expands rapidly, pressure food items that take up a significant part in drops, and food is aspirated into the mouth the animals' diet Fishes and larval salamanders: Excess water, Prehension - a method by which the animal gulped in with the food, exits via gill slits at the back of the mouth rapidly grasps the prey with its jaws or the process of seizing or grasping or otherwise Adult salamanders, frogs, and aquatic getting food into the mouth. In such animals, vertebrates: gill slits are absent, so excess the jaws are prey traps, designed to snare the water entering the mouth reverses its direction of flow to exit via the same route unwary 40 43  11/18/2024 Cont’d: Feeding in Air Swallowing the act of passing food from the Prehension does not always mouth, by way of the pharynx (or involve the jaws throat) and esophagus, to the stomach Jaws are used secondarily to help hold the struggling victim or Suspension feeders: the food-laden cords of mucus are swept by to deliver a killing bite synchronized ciliary action into the esophagus Birds of prey snatch quarry Other animals usually swallow prey with their talons whole or in large pieces Mammalian predators often Suction feeders: rapidly expand the use claws to catch and then buccal cavity repeatedly to work the captured prey backward into the control intended prey esophagus 44 45 Cont’d: Swallowing Cont’d: Swallowing Terrestrial vertebrates: use the tongue In many vertebrates: swallowing to reposition the food bolus and work it involves mastication (the chewing of toward the back of the mouth. food) Snakes: swallows a relatively large Within animals, mastication has animal by stepping the tooth-bearing had a profound influence upon skull bones over the dispatched prey design, producing an akinetic skull The highly kinetic skull of snakes with precise tooth occlusion and allows great freedom of jaw only two replacement sets of teeth, movement. a secondary palate, large jaw- closing musculature, and changes in lower jaw structure 46 47  11/18/2024 Introduction Two structural components combine to define the long axis of the Skeletal System: vertebrate body, offer sites for muscle attachment, prevent telescoping of the body, and support much of the weight The Axial Skeleton Notochord is a long, continuous rod of fibrous connective tissue wrapping a core of fluid or fluid-filled cells  Vertebral column consists of a discrete but repeating series of cartilaginous or bony elements The notochord is phylogenetically the oldest of the two structural components, but it tends to give way to the vertebral column, which assumes the role of body support in most later vertebrate 49 Basic Components: Vertebrae BASIC COMPONENTS  The first components of the vertebra to appear were the dorsal and ventral arches that rested upon the notochord  Vertebrae  The dorsal arches, neural and interneural (intercalary) arches, protected the neural tube  Ribs  The ventral arches, hemal and interhemal arches, enclosed blood vessels  Sternum  The second components is the formation of two  Gastralia centra: an intercentrum (hypocentrum) and a pleurocentrum.  The bases of the ventral arches expand to form these centra where they meet the notochord  The centra served to anchor and support these arches 50  11/18/2024 Vertebrae: Regions of the Vertebral Column Vertebrae: Regions of the Vertebral Column Each vertebral segment consists of Tetrapods: the trunk becomes further arches and centra: differentiated Up to two dorsal arches (neural and anteriorly into the neck, or cervical region interneural) posteriorly into the hip, or sacral region Two ventral arches (hemal and  In early tetrapods: a postsacral region of up to interhemal arches) five or six vertebrae, bearing the fused, two centra (intercentrum and proximal bases of their respective ribs, typically pleurocentrum) continues behind the sacral region  In some tetrapods: there is further Fishes: the vertebral column is differentiation of the trunk into the chest, or differentiated into two regions: the thoracic region and into the area between an anterior trunk region the thorax and the hips, the lumbar region posterior caudal region 11/18/2024 52 53 Vertebrae: Centrum Vertebrae: Centrum Each centrum constitutes the body of the Vertebral Types vertebra Aspidospondyly, all elements are aspondyly - centra may be absent separate specifically, the three arch monospondyly – one body elements (intercentrum, diplospondyly - two centra per segment pleurocentrum, and neural arch) The term means “cut-up spine,” a the pleurocentrum predominates and reference to the numerous separate becomes the body of each vertebral segment parts that constitute each vertebral the intercentrum becomes the intervertebral segment cartilage (disk) of the amniote vertebral Holospondyly, all vertebral elements column in a segment are fused into a single piece 55 11/18/2024 54  11/18/2024 Vertebrae: Centrum The centra are linked successively into a chain of Vertebrae: Centrum vertebrae, the axial column. The shapes of surfaces at the articular ends of the Procoelous - centra is concave anteriorly centra affect the properties of the vertebral and convex posteriorly column and the way in which forces are Opisthocoelous – The reverse shape, distributed between vertebrae concave posteriorly and convex anteriorly Acoelous - centra with flat ends and especially suited to receive and distribute compressive Heterocoelous - Centra that bear forces within the vertebral column saddle-shaped articular surfaces at both Amphicoelous – If each surface is concave and ends the centrum is design to allow limited motion in most directions 56 57 Vertebrae: Centrum Vertebrae: Centrum  Intervertebral disk in the adult is a pad of fibrocartilage whose gel-like core, the Centra Function nucleus pulposus, is derived from the A. Amphicoelous or acoelous centra flex about a embryonic notochord point on their rims, tending to stretch the  Intervertebral disks are found only in centrally located dorsal nerve cord mammals, in whom they reside between B. Opisthocoelous and procoelous centra eliminate successive surfaces of adjacent centra this potentially damaging stretching tendency with ball-and-socket ends that establish a  In other groups, the pad between centra is centrally located point of rotation instead of one called an intervertebral cartilage or body at the rims  Joining the rims of adjacent centra is the C. Heterocoelous centra, opposite, saddle-shaped intervertebral ligament, which is important surfaces fit together, allowing extensive lateral in controlling the stiffness of the vertebral and dorsoventral rotation column when it flexes 58 59  11/18/2024 Ribs  In tetrapods: ventral ribs are lost and the dorsal ribs, persists to become the trunk ribs of Ribs terrestrial vertebrates Ribs are struts that sometimes fuse with  Ribs of primitive tetrapods are bicipital, having vertebrae or articulate with them. two heads that articulate with the vertebrae Ribs provide sites for secure muscle  The ventral rib head, or capitulum, attachment, help suspend the body, articulates/joints with the parapophysis, a ventral form a protective case around viscera process on the intercentrum. (rib cage), and sometimes serve as  The dorsal head, or tuberculum, articulates with the diapophysis, a process on the neural arch accessory breathing devices In many fishes, there are two sets of ribs Although ribs function in locomotion in tetrapods, with each vertebral segment, a dorsal they become an increasingly important part of the and a ventral set respiratory system to move air through the lungs 60 61 Ribs Ribs In Reptiles Turtles: have no cervical ribs, and the True ribs - Ribs that meet ventrally with the ribs of the trunk are fused with the sternum costal plates of the carapace True ribs consist of two jointed segments The two sacral ribs are not fused with vertebral (costal) rib - a proximal segment the carapace articulated with the vertebrae Snakes: have long, curved ribs beginning sternal rib - a distal segment that is usually at the second vertebra and continuing cartilaginous and meets the sternum far into the tail False ribs – Ribs that articulate with each There is no sternum for ribs to attach to; other but not with the sternum however, the ventral ends of the ribs Floating ribs - Those false ribs articulating have ligamentous connections with with nothing ventrally integumentary scutes These ribs participate in locomotion 62  11/18/2024 Ribs Sternum In birds Sternum is a midventral skeletal structure that offers a site of origin for chest muscles  Cervical ribs are reduced and fused to the It also secures the ventral tips of true vertebrae. ribs to complete the protective  In the thoracic region, the first several ribs chondrified or ossified rib cage are floating ribs, followed by true ribs that Rib cage consists of ribs and sternal articulate with the sternum. elements that embrace the viscera.  Some floating and most true ribs bear Size and shape changes in the rib cage uncinate processes, projections that extend also act to compress or expand the posteriorly from proximal rib segments lungs, promoting ventilation  Uncinate processes, like the rib cage The sternum may consist of a single bony generally, offer sites of attachment for plate or several elements in series respiratory and shoulder muscles 64 65 Sternum Sternum Fishes, turtles, snakes, and many Anurans limbless lizards lack a sternum a single element, the xiphisternum, A sternum is absent in the first often tipped with the xiphoid fossil tetrapods, but it is present in cartilage, lies posterior to the modern amphibians pectoral girdle and in some, a In many urodeles: the sternum is a second element, the omosternum single midventral sternal plate capped by the episternal cartilage, grooved along its anterior borders lies anterior to the girdle to receive the ventral elements of the shoulder girdle, the procoracoid plate 66 67  11/18/2024 Sternum Sternum In flying birds In most mammals the massive flight muscles arise the sternum consists of a from a large sternum that bears a chain of ossified elements in prominent ventral keel, the carina series, the sternebrae The carina provides additional The first, manubrium and surface for muscle attachment last, xiphisternum, bears a cartilaginous or bony xiphoid process 68 69 Gastralia Gastralia the gastralia, or abdominal ribs, is a Turtles separately derived set of skeletal elements located posterior to the sternum in some the plastron is a composite bony plate vertebrates forming the floor of the shell the gastralia are of dermal origin Gastralia are restricted to the sides of the It consists of a fused group of ventral ventral body wall between sternum and dermal elements, including pelvis and do not articulate with the contributions from the clavicles vertebrae (epiplastrons) and interclavicle They are common in some lizards, (entoplastron) as well as dermal crocodiles, and Sphenodon elements from the abdominal region Serve as an accessory skeletal system that provides sites for muscle attachment and (possibly the gastralia) support for the abdomen 70 71  11/18/2024 FLUID ENVIRONMENT an organism does not depend primarily on the endoskeletal framework for support, instead, the body takes advantage of its buoyancy in the surrounding FORM and water For an active aquatic organism, two problems are uppermost 1. The drag on the body as it slips through a relatively FUNCTION dense medium, water. The answer is streamlining, contouring of the body to reduce drag forces The general body shapes of fast-swimming fishes are streamlined This shape improves the performance of fishes as they meet common physical demands while traveling through a medium that resists their passage 73 FLUID ENVIRONMENT TERRESTRIAL ENVIRONMENT 2. Orientation in three-dimensional space Problem: Gravity Any streamlined body has a tendency to tip and deviate from its line of travel, When remaining in place, the tetrapod’s body rotating about its center of mass. either rests on the ground between sprawled In fishes, these perturbations are legs, or it is suspended between the pairs of countered by stabilizing fins appropriately positioned along the body legs, as in most mammals Figure 9.3 The pairs of legs function as The body of a fish can deviate from its abutments/brace that support the body intended line of travel in three ways. between them A roll rocks the fish about its long The vertebral column serves as a bridge axis between the support posts, the legs, and A yaw swings it from side to side suspends the body from it A pitch bucks it up and down about its center of mass 74 75  11/18/2024 Regional Specialization in Tetrapod Columns Regional Specialization in Tetrapod Columns In tetrapods, the trunk becomes further In most fishes: the vertebral column is differentiated into two regions: an differentiated anteriorly into the neck, or anterior trunk region and a posterior cervical region, and posteriorly into the caudal region hip, or sacral region. The relatively undifferentiated vertebral There is further differentiation of the column of fishes reflects the fact that it trunk into the chest, or the thoracic is not used to support the body region, and into the area between the Support comes generally from the thorax and the hips, the lumbar region. buoyancy of the surrounding water. The vertebral column mainly offers sites of attachment for the swimming In most fishes, the vertebral column is musculature. differentiated into two regions: an It serves as a mechanical replacement anterior trunk region and a posterior of the notochord and allows lateral caudal region. flexibility for swimming Regional Specialization in Tetrapod Columns Regional Specialization in Tetrapod Columns In tetrapods Snakes: have the longest the vertebral column supports the body against columns with as many as gravity and receives and transmits the propulsive forces that limbs generate during locomotion 400 or more and almost no regional specialization Diverse functional demands are placed on the vertebral column, so we might expect to find Anurans: shortest columns delineation of specialized regions Birds and Turtles: only the 1. Sacral vertebrae- for locomotion and support cervical and caudal segments 2. Cervical vertebrae- to increase mobility of the are flexible head 3. Thoracic vertebrae- for external respiration Most of the trunk vertebrae 4. Lumbar Vertebrae- remaining segments are being rigidly fused to the anterior to the sacral vertebrae synsacrum in birds, and carapace in turtles  11/18/2024 The Craniovertebral Junction and Neck Vertebrae The Craniovertebral Junction and Neck Vertebrae Amphibians have one cervical vertebra. The Amniotes number is higher in reptiles and still higher in birds. Mammals typically have seven. the first two vertebrae are atlas and axis Amphibians The first vertebra, or atlas, is The first and only cervical vertebra of ringlike bone and lacks modern amphibians lacks processes centrum The absence of processes and the nature The centrum of the atlas has of the amphibian craniovertebral joint become the odontoid process permits limited dorsoventral rocking of of the second vertebra, or axis the skull The function is also not possible in A bony proatlas, resembling a neural fishes. arch is interposed between the skull and atlas in crocodilians The Craniovertebral Junction and Neck Vertebrae The Craniovertebral Junction and Neck Vertebrae Birds Cervical vertebrae are flexibly articulated to give the head great freedom of movement and Birds reach when a bird preens its feathers or probes for food Heterocelous centra, combined with the atlas-axis complex and The caudal ends of the centra the largest number of cervical are saddle-shaped, having a vertebrae in any tetrapod (12 convexity in the right-left axis commonly to 25 in swans) and a concavity in the enable some birds to turn their dorsoventral axis (vertebrae is heads 180 degrees to the rear, heterocelous) enlarging the arc of their horizon to that of a complete circle These vertebrae enable both lateral and dorsoventral flexion of the neck.  11/18/2024 The Craniovertebral Junction and SACRUM AND SYNSACRUM Neck Vertebrae SACRAL VERTEBRAE bear stout (bulky) transverse TURTLES processes to bear the thrust of the pelvic girdle Uniquely flexible neck. Amphibians- one sacral vertebra. Ball-and-socket joint in the living reptiles- have two. procelous centra, enable the entire head and neck to be most mammals- have three to five. retracted into the shell SACRUM - single bony complex formed when the sacral vertebrae of mammals ankylose MAMMALS SYNSACRUM - adult complex formed Always have seven cervical when the last thoracic vertebra, all vertebrae lumbars, sacrals, first few caudals and the ribs of modern birds ankylose (unite). Tail Vertebrae: Urostyle, Pygostyle, and Coccyx Tail Vertebrae Caudal vertebrae form a urostyle in Tetrapods anurans, a pygostyle in birds, and a coccyx in apes and humans numbered 50 or more Urostyle: It develops from a continuous elongated perichordal cartilage at the In modern ones, the number is much reduced and highly base of the larval tail, and it grows and variable. ossifies after the tail is lost at metamorphosis Tail end – arches and processes become progressively Pygostyle: the skeleton of the visible part shorter and rudimentary. of the tail. - The pygostyle develops as 4 separate cartilaginous centra. Coccyx – “tailbone“ - The centra of the coccyx are still identifiable, but the last one is a mere nodule of bone.