Integumentary Template PDF

Integumentary & Skeletal Systems The Integument: Embryonic origins Epidermis from single-layered surface ectoderm (outermost layer of cell) ○ Stratum germinativum – replenishes periderm (outer layer of tissue) Dermis from several sources ○ Mainly dermatome ○ Somites produce sclerotome medially; derm...

Integumentary & Skeletal Systems The Integument: Embryonic origins Epidermis from single-layered surface ectoderm (outermost layer of cell) ○ Stratum germinativum – replenishes periderm (outer layer of tissue) Dermis from several sources ○ Mainly dermatome ○ Somites produce sclerotome medially; dermomyotome laterally ○ Dermomyotome outer wall spreads under ectoderm to form connective tissue of dermis Largest organ (~15% of body weight) Large surface area in humans (1.5-2 m^2) Composed of 2 layers 1. Epidermis: keratinized stratified squamous epithelium a. Can make skin more thick because of kalyo b. Similar to squares 2. Dermis: connective tissue layer 3. Hypodermis: below Variable thickness (1-2 mm) ○ Dermis up to 6 mm Protection (trauma, fluid loss, chemical attacks, UV, infection) ○ Acidic nature maintains bacterial communities in check Dandruff: our immune system would react and shave this off Sensory (touch, pressure, pain, temperature) Thermoregulation (insulation, evaporative coolings) ○ Sweating when it’s hot to lose heat Vitamin D3 synthesis Excretion of salts, water, organic wastes Gas exchange (for amphibians) Nonverbal communication ○ Pheromones → to warn predators General features: Dermis Dermal bones – produced through intramembranous ossification (within the membrane + dermis) ○ Placoderms, some mammals (e.g., armadillos) Plies – collagen fibers woven into layers ○ Cloth fabric-like allows bending but resists distortions in body shape (essentially stretches to a certain degree) Dermis contributes to the structural integrity Mucus production prevents desiccation (drying up) ○ Fishes – bacterial infection protection, laminar flow (fluid is all flowing in parallel streams) To be more hydrodynamic → streamlined ○ Lissamphibia – bacterial infection protection, prevents desiccation ○ Mucous gland – slimy coating for some animals, very slimy ○ Granular gland – secrete substances for toxin & repellant for defense mechanism Stratum corneum – outermost layer; keratinized ○ Keratinization – accumulation of keratin from dying epidermal cells Produced by keratinocytes Alpha (soft) – flexible (when your callus is soft + flexible) Beta (hard) – specializations Form protein keratin ○ Callus – thick protective keratinized layer Faster accumulation + formed due to stratum corneum Specializations with beta keratin Phylogeny: Agnatha No layer of dead cells = no keratinization in almost all cells ○ Horny teeth (lampreys) Slime glands – row of ducts ventrally along the body ○ Copious slime production Diverse integuments of fishes 1. Photophores (light-emitting organs) ‘Slime Eel incident explosion on Highway after bizarree traffic incident’ ○ Essentially a lot of hagfish slime covered an entire car in their mucus Phylogeny: Fishes No layer of dead cells = no keratinization in almost all cells Mucus production Two cell types ○ Epidermal cells – line the outermost ○ Unicellular glands – specialized cells Club cell – Excitation (alarm/fear) Granular cell – mix with bitter compound Goblet cell – mucus production Sacciform cell – Deterrent chemicals ○ The last two secrete compound predator repellent + not directly touching the scale but the epidermis ○ Alarm cells – pheromones + non verbal communication 2. Camouflage (PVC Dragon → Australia) 3. Chromatophores (pigment-bearing cells → to blend in) (e.g. Tampalpuke or flat fishes) 4. Guanine crystals (reflect light at certain angles) 1. Chondrichthyes Dermal bone absent Placoid scales present (first type of scale) Develops in dermis; projects through epidermis ○ Tip made of enamel; pulp cavity within ○ Controls wake formation during swimming Allows the shark to be more hydrodynamic Dermis with fabric-like arrangement of fibrous connective tissue 1. ○ Isopedine – dense lamellar base 2. Spongy vascular bone Outer surface – dentin (cosmine) with layer of enamel 2. Ganoid scales (Polypteriformes, Gars) ○ Thick enamel (ganoine) surface layer ○ Modified cosmoid scales ○ Cosmine replaced by dentine ○ Rhomboid in appearance 2. Bony fishes Dermis divided into superficial loose connective tissue & dense fibrous connective tissue Dermal scales do not pierce slime-coated epidermis 3. Cycloid and ctenoid scales (Teleostei) ○ Cycloid scales with concentric rings (circuli) ○ Ctenoid scales with posterior projections (ctenii) The same fish can have 2 different scales 1. Cosmoid scales (Fossil coelacanths & lungfishes) ○ Two basal bone layers Phylogeny: Tetrapods Recall: Amphibians metamorphose to terrestrial form Dermal scales only present in Apoda ○ Caecilians and tailed amphibians Skin specialized as respiratory surface for gas exchange ○ Capillary beds in lower epidermis Urodela rely on cutaneous respiration (gas exchange across skin) 1. Amphibians (fully aquatic in lifestyle) Aquatic larval Urodela ○ Leydig cells for protection against microbes + against infections / substances in water Adult Urodela ○ Nuptial pads on digits of males Highly keratinized Calluses of cornified epidermis Mucus and poison glands on dermis Chromatophores in epidermis but mostly in dermis → pigment-bearing cells Capillary beds reach to lower epidermis for respiration 2. Reptiles Extensive keratinization; fewer skin glands ○ Compared to fishes – scales → dermis Scales from folded epidermis ○ Hinge – flexible junction bet. Scales SPECIALIZED SCALES Scutes – large plate like scales Gastralia – dermal bones in abdominal area Osteodermis – epidermis-supporting dermal bones (shed molting) 3 Average Feather Types 1. Pennaceous feathers (A + B): has a stalk/quill 2. Plumulaceous feathers: has no vanes a. A down feather b. Filoplumes 3. Birds Feathers form from epidermal-dermis interactions Dermis highly vascularized ○ Allows body heat to be or move in contact with the eggs Stratum corneum with highly keratinized surface Uropygial gland → water repellant coating ○ Raincoat of birds ○ Secretes lipids and puts in on the feathers (don't to repel water → reason why water and oil don’t mix) Salt glands → salt excretion ○ Bottom right picture is beta! Embryonic induction → interaction of dermis stimulates epidermis Feather growth During development: pulp caps & sheath are shed Feather colors Barbule shape: smaller structure within each barb ○ Much of iridescence is structural in nature → not chemical Airplane wings were inspired by feathers → to be more aerodynamic due to air resistance Feather evolution Feather-like scales, teeth, hair, bony scales develop from epithelial-mesenchymal interactions 4. Mammals Epidermis localized specially as hair/nails/glands ○ Epidermis + dermis interaction specialized Keratinocytes as epithelial cells of epidermis ○ Forms callus with extensive keratinization Replacement cells from stratum basale/germinativum ○ Nagbabalat, so it replaces this → upward movement Other cell types in epidermis ○ Langerhans cells – stellate; immune system-related ○ Merkel cells – mechanoreceptors ○ Chromatophores – melanin secretion → skin color Skin color: melanin from chromatophores + yellow stratum corneum + red from blood vessels ○ Yellow stratum corneum is like when pedicured Hair matrix – starts keratinization within follicle (localized) All of the above acts as a segway into muscles Arrector pili – smooth muscle; makes hair stand (fear, cold, anger) ○ Controlling hair filaments, goosebumps (e.g. cats hair going up) Melanin will regenerate less once you grow older, but it happens slowly ○ Dermis double-layered ○ Papillary layer – fingerlike projections into epidermis Dermal papillae ○ Reticular layer – anchors dermis to fascia Dermal bones rare (e.g., Glyptodon, armadillo) Fibrous connective tissue – elasticity ○ Pinching → returns back unless old age Thick fur/pelage in many mammals; two layers include: ○ Guard hairs – larger, coarse, outer ○ Underfur – finer, shorter, underneath guard hairs Grain – directionality of hair ○ Punyot! bunburian! Hair as slender keratinous filaments ○ Root – base ○ Shaft – post-root length to tip ○ Cuticle – outermost scaly cover ○ Hair cortex (central layer) and medulla (central most part) ○ Follicle – rooted in dermis ○ Hair papilla Three gland types in integument 1. Sebaceous – globular; sac-like (pouch-like structures) a. Produces sebum (oils, lipids) i. Waterproofing; lubrication → so we don’t dry b. Absent in palms/soles of feet 2. Eccrine – long, coiled invaginations of epidermis into dermis a. Thin, watery fluids b. Not associated with hair follicles c. Innervated by cholinergic nerves d. Found in epidermis 3. Apocrine – long, coiled invaginations of epidermis into dermis a. Viscous, lipid-containing fluids i. So has oil due to lipids b. Associated with hair follicles c. Chemical signaling d. Innervated by adrenergic nerves e. Body odor → non verbal communication f. Sweat gland – derived from eccrine glands in humans i. Form of Evaporative cooling (like when you blow it) ii. Social communication Mammary glands ○ Milk (watery mixture of fats/carbs/proteins) ○ Form from ectodermal mammary ridges Outermost cell layer ○ Lactation – release of milk to young Horns, nails, claws Unguis is the outer layer In the subunguis ○ Layer of keratin ○ Growing parallel to nail bed (the whole structure) Why do we have nails? ○ Protects digit from mechanical injury ○ Biomechanics → provide a very hard surface to counter the force in soft surface Try pushing a button! The nail bed pushes upward, so you won’t feel any additional hard force Claws grow in a curve direction Horns and antlers Horns grows from stratum corneum The yellow part is their stratum corneum keratinizing → going up Some can regrow their horns Horns don’t split/branch compared to antlers Has bony core They have bony cores too, but they have “velvet” or a coat of blood vessels, skin and short hair that supplies nutrients and minerals to the growing bone. Stratum corneum do not keratinized upward, but the bone can get cut off and grow back again Male moose can shed its own antlers → after mating season, the bony core forms an abscission line to shed Types of Horns 1. True horns a. In Bovidae b. Bony core, keratinized sheath 2. Pronghorn a. Keratinized sheath in pronghorns shed in winter b. Only present during winter time 3. Giraffe horns a. From ossified cartilaginous processes (cartilage); living non cornified skin 4. Rhinoceros horn a. Horn from keratinous fibers b. For very tough nails, you could see the fiber c. No tissue found = no wound Baleen Bone & Cartilage Cartilage Found in joints, knee caps, ears, & more Semi-transparent connective tissue covered by perichondrium ○ Perichondrium: Peri = outer perimeter Chondrium = chondrocyte Outermost covering/layer With chondrocytes: ○ Anything cartilage related ○ Get different types of cartilages based on the different proportions of the substances Collagenous extracellular matrix Elastic fibers Proteoglycan-rich substance Main skeletal tissue in chondrichthyans & early ontogenetic development (embryo) Perichondral & endochondral ossification in Osteichthyes: alongside edges of each structure Elastic cartilage: ears Hyaline cartilage: joints Fibrocartilage: joints, more stiff, in pelvic girdle where genitals are If a whole structure is layered with cartilage: ○ Stiffer ○ Can withstand more chemical stress Calcified cartilage: ○ From deposition of calcium salts inside hyaline cartilage/fibrocartilage ○ Jaw of megalodon made from the same calcified cartilage Bone Not entirely solid Composed of canals & cells interacting to form the bone matrix Collagenous fiber matrix + spaces ○ Filled with hydroxyapatite crystals Cemented b water & mucopolysaccharides Osteocytes: ○ Trapped in lacunae: canal/inner holding area that’s connected to 1 another ○ Connected by canaliculi: canals ○ Produce cement -picBone Types (a) Compact bone With Haversian system parallel to long axis of bone ○ Haversian system: Unique to amniotes (reptiles, birds, mammals) Periosteum: Thin layering that covers most bone surfaces except articulating surfaces (areas in contact with joints) ○ Periosteal bone Haversian canal: ○ Arteriole ○ Venule ○ Lymph vessel (b) Spongy bone Trabeculae + marrow ○ Marrow: Blood vessels = red marrow Adipose tissue = yellow marrow Connective fibers with blood vessels, nerve fibers, adipose tissue Lined by endosteum (inside bone) Dentin: ○ Odontoblasts retreat with dentin production ○ Dentinal tubules (canaliculi): sticks them together ○ Dentin layer of teeth are not living cells Overview ○ -picJaws Supports gills Attachment for respiratory muscles In gnathostomes it forms: ○ Jaws ○ Hyoid apparatus: tongue-supporting structure Arises from neural crest cells Derived from branchial basket Appeared 1st in acanthodians & placoderms Splanchnocranium supported pharynx roof & lateral pharyngeal slits Arose from anterior pair of gill arches ○ Serial development of jaws & branchial arches ○ Similar nerve & blood vessel distribution ○ Jaw muscle modified from branchial arch musculature ○ Muscles that control jaws: derived from muscles that control pharyngeal slits -pic- Serial Theory Composite Theory Mandibular Arch Origin 1st & 2nd branchial arch Fusion of premandibular & mandibular arch (1st 2 arches) Hyoid arch origin 3rd succeeding arch Epibranchial, ceratobranchial, hypobranchial elements of 3rd gill arch Rest of branchial arch Rest of arches Rest of arches -pic Chondrocranium Encloses & supports brain in elasmobranchs ○ Made of cartilage Embryonic structure only in other vertebrates ○ Partially/entirely ossified ○ Scaffold for developing brain ○ Supports sensory capsules Holds eyes & developing sensory organs ○ Earliest stage -> slowly becomes ossified Arises from neural crest cells Splanchnocranium Ancient structure ○ Associated with feeding surfaces in amphioxi (gills, pharyngeal slits) -picJaw Attachments Agnatha = paleostylic ○ None of arches attaches to skull -pic Placoderms & acanthodians = euautostylic ○ Mandibular arch suspended from skull itself Early sharks, some osteichthyans, rhipistidians = amphistylic ○ 2 primary articulations ○ Palatoquadrate (upper jaw) anteriorly ○ Hyomandibula posteriorly Most modern bony fishes = hyostylic ○ Mandibular arch attaches to braincase via hyomandibula Most amphibians, reptiles, & birds = metautostylic ○ Jaws attach to braincase via quadrate ○ Hyomandibular forms stapes ○ Hyoid from 2nd & 3rd arch supports tongue & mouth floor Mammals = craniostylic ○ Upper jaw part of brain case ○ Lower jaw suspended from dermal squamosal ○ Lower jaw not completely attached to upper jaw ○ Mammals don’t have specialized structures for attaching to jaw -picDermatocranium External-most bones Intramembranous ossification of mesenchymal/ectomesenchymal tissues of dermis Dermal bones contributing to skull ○ 1st associated with skull in Ostracodermi Forms sides & roof of skull Bony lining of mouth roof: encases splanchnocranium Teeth -picParts of Dermatocranium Facial Series Forms snout Septomaxilla: ○ Contributes to nasal cavity when present ○ Very thin bone ○ Present in some lineages only Purple-colored areas in diagram -picOrbital Series Dermal bones encircling eye Nasolacrimal tear ducts: ventral to eye Scleral ossicles: inside orbit Red-colored areas in diagram -picTemporal Series Sides of vertebrate head Posterior wall of braincase Fenestrae associated with jaw musculature Cheek formed by squamosal & quadratojugal Green-colored areas in diagram -picVault Series Forming dorsal covering = frontal, parietal, & post-parietal Roofing bones Parietal bones sometimes with parietal foramen (houses pineal gland) ○ Pineal gland: light-detecting endocrine gland Palatal Series Forms floor of braincase Roof of mouth Teeth may be present on bones Parasphenoid (unpaired medial bone): in fishes & lower tetrapods Mandibular Series Lower jaw Encloses Meckel’s cartilage L & R joined anteriorly by mandibular symphysis (fissure, point of attachment) ○ Firm: arched unit ○ Soft: independent movement of mandible (e.g. snakes) ○ Can’t easily separate L & R mandible Overview of Skull Morphology Braincase Produced by chondrocranium Cartilaginous in cartilaginous fishes: no dermatocranium Extensive ossification in bony fishes -pic Sphenoid bones: ○ Close braincase wall posteriorly except for foramen magnum Occipital condyle: articulates (connects) skull with vertebral columm Otic capsule: ○ Opisthoic + prootic on posterior part ○ Encloses ear sensory organs Splanchnocranium -> epipterygoid/alisphenoid & middle ear bones -picJaws Upper Jaws Endoskeletal palatoquadrate in primitive vertebrates Palatoquadrate fully functional chondrichthyans Epipterygoid, quadrate in bony fishes & tetrapods Maxilla, premaxilla replace palatoquadrate in mammals ○ Maxilla & premaxilla: primary elements of jaws in mammals -picLower Jaw/Mandible Meckel’s cartilage: ○ In chondrichthyans ○ Enclosed in dermatocranium in fishes Articular bone: ○ Protrudes from exoskeletal case in fishes & most tetrapods ○ Articulates with connecting bones like hyomandibula -pic Replaces articular Dermal dentary: ○ Main bone comprising jaw ○ In mammals: forms condyle posteriorly ○ Articulates with glenoid fossa of temporal -picHyoid Apparatus Posterior to jaw Derivative of splanchnocranium behind jaws Supports: ○ Floor of mouth in fishes ○ Hyoid arch & some branchial arches ○ Gill arches Reduces hyoid apparatus in larval/paedomorphic amphibians ○ Lost in terrestrial adults ○ Some elements form tongue support Styloid process in many mammals ○ Distal end of hyoid horn fused with otic region -picCranial Kinesis (Skull movement) Kinetic Skulls Can move to some degree ○ Skull elements ○ Jaw elements ○ Hyoid arch Can protrude jaws When jaws open: negative pressure in mouth -> force water to go in -picAkinetic Skulls In mammals No movement in skull elements Allows suckling in infants Chewing with specialized teeth ○ As you chew: apply upward pressure Hard to counterbalance any pressure going against skull Fused cranium: refuse upward pressure No palatoquadrate -picPhylogeny of the Skull Chondrichthyes No ossification (Almost) no bone Chondrocranium more prominent Braincase = ethmoid + orbital + post oticooccipital Amphistylic ○ Ceratohyal + Meckel’s cartilage ○ -pic Ligament from base of nasal cap. To orbital process of palatoquadrate Feeding & jaw protrusion Movement of different splanchnocranium elements as it feeds: ○ Hyomandibula = ventral ○ Palatoquadrate = ? Nictitating membrane = very thin in the ventral margin of eye -picActinopterygii High degree of kinesis Opercular series covered gill arches Better mandibular support by hyoid arch ○ Hyoid arch: supports lower jaw Vacuum created during suction feeding by musculature & kinetic jaws ○ Suction feeding: creates negative pressure in buccal cavity More kinetic skull bone movement in derived actinopterygians ○ Neurocranium raised when they feed ○ Mandible lowered ○ Jaw arrangement allow protrusion -picPharyngognathy Pharyn = pharynx; mouth Gnathy = jaw Pharyngeal jaw: ○ Derived from gill arch bones & musculature ○ Jaw within a jaw ○ Process food -> smaller components ○ Musculature: chews food a 2nd time -pic 2nd set of crushing Helpful when feeding on very hard substrate Allows them to hold onto prey Sarcopterygii Lobe-finned fishes Palatoquadrate fused to ossified braincase in early lungfishes Labyrinthodont teeth (infolded) Paired nasal sacs in nasal capsules open into mouth via choana (internal naris) -> flows to pharynx ○ External naris opens nasal sacs to outside Nasolacrimal duct: ○ Drains secretion from lacrimal gland ○ Gets the excess of tears/extra secretion ○ Runs through nasal & lacrimal glands -picEarly Tetrapoda Lateral line system in skull of aquatic larvae Dermal bones fused/lost in modern Lissamphibia ○ Compact & firmly ossified bones in Caecilia ○ Urodela: Chondrocranium primarily orbitosphenoid & prootic Exoccpitals close braincase posteriorly ○ Anura: Highly variable ossification Paired prootics & exoccipitals + sphenethmoid Reduced splanchnocranium: very thin, some are reduced in size Hyomandibula doesn’t suspend jaw -picEarly Amniotes Skull roof formed from dermatocranium ○ Specifically parietal & some parts of temporal ○ Openings for eyes, pineal gland, nostrils Strong jaw-closing muscles move jaws Palatoquadrate reduced Epipterygoid + quadrate Hyoid arch produces stapes ○ Hyoid arch = smaller, more incorporated into rest of skull ○ Stapes = part of lower ear -pic-pic-picModern Reptilia Testudines (turtles): ○ Anapsid skull ○ Keratinized tooth plates on jaws Sphenodon: ○ Upper & lower temporal bars join front & back of lateral wall Squamata: ○ Loss of lower temporal bars allows streptostyly ○ Snakes: Mandibular symphysis joined by tissues Connects with lower jaw Allows them to move L & R mandibles further away from each other Unhinging from independent movement of kinematic chains & outward flaring of flexible joints -picAves Diapsid skull but modified Expanded brain & braincase Reduced palatal bones; epipterygoids lost Beak: ○ Drawn-out jaws ○ Keratinized Slider-crank mechanism Paleognath birdsL pterygoids slide on basipterygoid process Rhynchokinesis: flexions within beak allow parting of without mouth fully opening -picSynapsida - Mammalia Highly modified synapsid skull Dermal elements lost in therian mammals Postparietals fused -> interparietal in therapsids Monotremata: ○ Lack lacrimal ○ Small jugal bones ○ Tympanic ring around ear bones Auditory bulla: encloses middle ear ossicle in eutherians -picMammalia-Eutheria Occipital bone fused basioccpital, paired exoccipitals, supraoccipital, & interparietal Ventral bilobed occipital condyle articulates with atlas (1st vertebra) Nuchal crest: attaches neck muscles & ligaments Cribiform plate: between cranial cavity & nasal area Stapes: ○ From hyomandibula ○ Supported by malleus & incus -picMammalia Secondary palate aids in mastication ○ Hard palate = premaxillary, maxillary, palatal processes ○ Soft palate Mastication without impeding breathing Akinetic skull: ○ Allows precise strong occlusion of teeth ○ Mandibular condyle articulates precisely with squamosal bone Diphyodonty: “milk” & “permanent” teeth ○ Some mammals are polyphodonts -pic Axial skeleton Long axis of vertebrate body Oriented horizontally Upright - oriented vertically Components: Notochord ○ Core of fluid-filled cells enclosed in rod of fibrous connective tissue ○ First occured in the Protochordates (more primitive/older structure) Vertebral Column ○ Discrete repeating cartilaginous/bony elements Protovertebrae in Haikouella, Haikouichthys In younger, extinct fishes, first iterations of those elements Basic Components: - Heteronomous Segmentation repeating structures but not entirely similar as it runs across - Serial nature of vertebral column, repeating elements Neural tube ○ Also called Dorsal Nerve Cord ○ protected by neural+interneural and hemal+interhemal arches Neural and Hemal Arches enclose notochord Interrneural Arch Integrates neural arch Interhemal arch Integrates hemal arch Intercentrum and procentrum anchor ventral arches ○ Centra Anchors arch to notochord Caudal - Associated with the tail Sacrals Lumbars - waist area Thoracic vertebrae - Protects Viscera Cervicals - Head movements Gastralia Thoracic ribs Sternum Procoracoid Interclavicle Cervical ribs More localized specializations depending on the region of the body More specializations for more challenges - resisting gravity & staying upright ○ Centra (Body of vertebra) Based on number of Centra Aspondyly No centra in vertebra Monospondyly One centrum Diplospondyly Two centrum Polyspondyly Three/more centra Based on elements and how they are fused Aspidospondyly Centra and arches separate Holospondyly Fused vertebral elements per segment Based on the shape/appearance of the vertebra/intervertebral disc - notochord Acoelous - flate ends No articulating surfaces, higher stress/tension on notochord Amphicoelous Concave ends Both anterior & posterior ends are concave Protocoelous Concave anterior Opisthocoelous Concave posterior Heterocoelous Saddle-shaped articular ends Intervertebral disc not extended Vertebrae with articulating portions, the point of rotation is closer to the middle, doesnt need to stretch out as far as the Acoelous centrum - like ball & socket Ribs Allows better articulation Attaches muscles Protects viscera Accessory breathing devices ○ Allows flexibility - helpful for breathing, allow for changes in shape/volume of the lung cavity 2 types of Fish ribs 1. Dorsal Rib/Epipleural Ribs ○ Attaches to myomeres/myosepta 2. Ventral Rib/Pleural Ribs ○ Attaches to the body wall, interacts with the Pleural cavity First caudal vertebrae Fusion of hemal arches and formation of hemal canal True Ribs Ribs articulating with sternum Allows for compensation of volume & changes of size in cavity during respiration ○ Costal+sternal segments ○ Expansion and compression during breathing Capitulum Articulates with the parapophysis Anterior-mosts process that articulates with the vertebra Tuberculum Articulates with diapophysis Intercentrum Lost in amniotes ○ Capitulum articles with pleurocentrum (reptiles and birds) ○ Capitulum articulates between centra (mammals) False Ribs Ribs articulating with nothing ventrally Removed during some cosmetic surgeries Sternum Middle portion where two ribs articulate in the ventral position Sternum Rib Cage Sternum + Sternal Elemnts Fishes without sternum Urodela Sternal plate Anura Xiphisternum with xiphoid cartilage; omosternum ○ Omosternum: anterior portion of the xihisternum Turtles/Snakes/limbless lizards No sternum Other reptiles SIngle midventral element Birds Sternum with prominent carina ○ Carina: very enlarges/prominent structure, expanded sternum, keel/hull-like shape