Appendicular Skeleton PDF

11/25/2024 Basic Components Paired fins or limbs and the girdles the braces within the body that support them...

11/25/2024 Basic Components Paired fins or limbs and the girdles the braces within the body that support them The anterior girdle: shoulder or pectoral girdle Skeletal System: dermal and endochondral skeletal elements supports a pectoral fin or limb The Appendicular The posterior girdle: hip or pelvic girdle Skeleton consisting of endochondral skeletal elements support the pelvic fin or limb Pectoral Girdle Pectoral Girdle A pectoral girdle is a skeletal complex in the body wall immediately behind the head Clavicles occur in all classes of that articulates with the anterior fins or limbs bony vertebrates but are best developed in tetrapod consisted of three pairs of replacement bones that were part of the endoskeleton: Bony fishes have tended to lose coracoids, scapulae and the replacement bones of the suprascapulae pectoral girdle. four pairs of dermal bones: clavicles, supracleithra, Tetrapods have tended to lose posttemporal, postcleithra) derived dermal bones from dermal armor  11/25/2024 Note: very light grey: scapula Pectoral Girdle light grey: coracoid Pectoral Girdle dark grey: procoracoid In modern amphibians: the dermal bones are usually lost entirely (salamanders) or reduced in prominence (frogs) The endoskeletal scapuloprocoracoid (is the unit of the pectoral girdle that contains the coracoid and scapula) becomes the predominant girdle element, yet retains its fidelity to the cleithrum Tetrapods carry over from rhipidistians (extinct lobed finned fishes) a shoulder girdle consisting of dermal and endoskeletal elements: however, tetrapods have a shoulder girdle that is In fishes: the scapulocoracoid tends to be a single structurally and functionally detached from the skull -> the dorsal series of dermal bones are element lost In early tetrapods: the connecting skull bone, the posttemporal, and adjoining shoulder bones, supracleithrum and postcleithrum (= anocleithrum), are absent, leaving a dermal shoulder girdle In primitive amniotes: the clavicle and composed of the remaining ventral elements: the paired cleithrum and clavicle, and an unpaired interclavicle persist, but the cleithrum is usually midventral interclavicle that joins both halves of the girdle across the midline absent **the dermal elements (no shading) endochondral elements (shaded elements)** Note: very light grey: scapula Note: very light grey: scapula Pectoral Girdle Pectoral Girdle light grey: coracoid light grey: coracoid dark grey: procoracoid dark grey: procoracoid **the dermal elements (no shading) endochondral elements Modern Reptiles (shaded elements)** Birds Replacement bones the clavicle is lost but it is retained in many Replacement bones In turtles it is incorporated into the plastron as the the paired clavicle usually fuses with the entoplastron Dermal bones unpaired interclavicle, producing the the endochondral three-part shoulder girdle is also retained composite wishbone, or furcula but its evolution becomes complicated in derived groups. Both scapula and procoracoid of the In turtles: a distinct scapula and distinct coracoid are endochondral girdle persist present. In most lizards: all three elements are present— scapula, coracoid, procoracoid —although the Dermal bones procoracoid is reduced to more of a process joined to the Procoracoid may contribute to the other bones portion of the scapula around the glenoid Among other reptiles, a scapula and a coracoid are fossa and to one end of the coracoid as present in the ossified skeleton, but the procoracoid has the procoracoid process various fates. **the dermal elements (no shading) endochondral elements (shaded elements)**  11/25/2024 Note: very light grey: scapula light grey: coracoid Pectoral Girdle dark grey: procoracoid **the dermal elements (no Synapsids shading) endochondral elements (shaded elements)** Pectoral Girdle Replacement bones  this three-part shoulder girdle is retained in Clavicle/ Collar bone – is a bone that serves as pelycosaurs, therapsids, and monotreme a strut between the shoulder blade and mammals. the sternum (breastbone)  In therian mammals: the procoracoid becomes vestigial (marsupials) or incorporated into the Mammalian clavicle is large in insectivores and manubrium of the sternum (eutherians). primates and in mammals with strong forelimbs that are  The coracoid becomes reduced and joins the used for digging, climbing or flying. scapula as the coracoid process On the other hand, there are mammals whose skeleto- Dermal bones muscular system has undergone adaptations that have  The clavicle and interclavicle are present in reduced the clavicle to a mere splinter (cat) or eliminated therapsids and monotremes, but in marsupials it altogether (cetaceans, ungulates) and eutherians, the interclavicle is absent, the clavicle often is reduced in size, and the scapula In cats, the clavicle is a vestigial splinter reaching becomes the predominant shoulder element neither the sternum nor the scapula  the coracoid is reduced and fused to the scapula as the coracoid process Pelvic Girdle Pelvic Girdle A bony or cartilaginous structure in Fishes vertebrates, attached to and supporting pelvic girdle consists of 2 cartilaginous or bony plates (ischiopubic the hind limbs or fins plates) that articulate with the pelvic fins Pelvic plates (black) No dermal components Composed of a single bone with three parts: pubis, ischium, and ilium At the junction of the pubis, ischium and ilium, a socket, the acetabulum accommodates the head of the femur.  11/25/2024 Pelvic Girdle Pelvic Girdle Birds Ilium & ischium expanded to Tetrapods accommodate musculature needed for bipedal locomotion Pair of cartilaginous plates (walking on two legs in an form in embryos & each upright position) ossifies at 2 centers to Girdle is braced against lumbar form: pubis & ischium & sacral vertebrae An additional blastema Pubis bones are typically gives rise to the ilium reduced (long but thin) the limited pubic symphysis provides a larger outlet for eggs Pelvic Girdle Fins are membranous or webbed processes internally strengthened by radiating and thin fin rays Mammals They form initially at the interface between dermis and epidermis but then sink into the The ilium, ischium and pubis dermis (dermal fin rays) ankylose early in postnatal life to form a left and right innominate bone/ hip Function bone Steering devices for changing directions Stabilizers Slows or halt forward thrust Plays minimal role in forward thrust  11/25/2024 Fins Fins The proximal part of the fin 1. Fin Rays close to the body is Ceratotrichia - found in cartilaginous supported by fishes. These are long horny rays pterygiophores composed of a material similar to what Two types: composes the dorsal spines of spiny Basals sharks Radials - extend support from the basals into the Lepidotrichia - found in bony fishes and middle region of the fin consist of jointed bony dermal scales aligned end to end Fins occur singly, except for usually an ossified or chondrified series of a pair near the head tiny elements that strengthen this web (pectoral fin) and a second Actinotrichia – found in some bony pair posterior to this (pelvic fishes. The tip of the fin may be further fins) stiffened by additional keratinized rods Fins Fins 2. Paired Fins 2. Paired Fins Three categories of Paired fins classification of paired fins is based Lobed fins - generally consist of a on what girdle they are attached. fleshy proximal portion (lobe) containing the skeleton and its Pectoral fins are braced against the attached muscles, and a glenoid fossa or glenoid region of membranous distal portion that is the scapula and coracoid. stiffened by fin rays. Pelvic fins are braced against a The fin resembles a paddle and prominence on the lateral or arises from a narrow base. posterior aspect of the pelvic plate Lobed fins are characteristic of dipnoans and crossopterygians  11/25/2024 Fins Fins 2. Paired Fins Three categories of Paired fins 2. Paired Fins Fin Fold Fins - characteristic of Three categories of Paired fins cartilaginous fishes, have broad Ray Fins - The rays lepidotrichia are the same as those base. other bony fishes It is broad in modern sharks and With reduction of the basal skeleton during time, fins have was broader in Paleozoic. become increasingly flexible and a number of species have The pectoral fins of cartilaginous lost their pelvic fins. fishes, ancient and modern exhibit a wide diversity of skeletal morphology. Fins 3. Median Fin Fins Fishes have one or more median dorsal fins and many have midventral anal fin just behind the anus. Median fins act as keels, keeping motionless fishes from rolling to the 4. Caudal Fins left and right. used for propulsion during locomotion in fishes Median dorsal fins- are unpaired median fin on the backs of fishes and some other aquatic vertebrates Caudal fins are classified on the basis of direction taken by the terminal portion of the notochord, vertebral column and their shape  11/25/2024 Diphycercal Fins Fins 4. Caudal Fins 4. Caudal Fins Caudal fins can exist from different conditions Variants of heterocercal condition Heterocercal - if the tail contains dorsal and ventral lobes and if the notochord Diphycercal- if the vertebral column ends with Homocercal turns upward into a larger dorsal lobe very little upbending. Present in Paleozoic sharks Common in dipnoans and Latimeria Hypocercal - a rare condition in which Homocercal- a caudal fin composed of two the vertebral column turns downward lobes of equal proportion Hypocercal Embryonic Development of Tetrapod Limbs Limbs Formally termed as Chiridium PATTERN: characterized by the predominance of elements arising posteriorly on the a muscular appendage with well-defined postaxial side of the limb. joints bearing digits (fingers and toes), not a fin, at its end. 1. A stylopodium appears, which consists of a single proximal element (humerus or femur). Three recognized regions Autopodium = the distal end of the limb; 2. The stylopodium subsequently branches to yield an adjacent set of preaxial (radius the wrist and ankle, which in turn or tibia) and postaxial (ulna or fibula) elements that represent the intermediate support their respective digits section of the limb, the zeugopodium Zeugopodium = middle limb region; ulna A depression within the 3. Through subdivision and budding of embryonic primordia, the postaxial element and radius of the forearm, tibia and pectoral girdle, the glenoid fossa, alone extends the emerging embryonic pattern farther distally, forming most of the fibula of the shank. primordia of the autopodium (manus or pes), which includes all the digits articulates with the humerus. Stylopodium = limb region closest to the A deep socket in the pelvis, the 4. The preaxial element contributes only a few wrist or ankle elements but none of body; humerus of the upper arm, femur the digits to the emerging embryonic autopodium acetabulum, receives the femur. of the thigh  11/25/2024 Embryonic Development of Tetrapod Embryonic Development of Tetrapod The preaxial element (radius/tibia) does not branch but gives rise to more distal elements contributing to the autopodium. Limbs Limbs The postaxial element (ulna/fibula) branches to form the carpals or tarsals and the digital arch, which yields the fingers and toes. This postaxial side of the limb is thought to be derived from the metapterygial stem of fishes. The wrist (carpus) of a Manus/ HAND generalized pentadactyl The wrist, palm, and digits constitute a functional (having five toes or fingers) unit - the hand (manus) hand consists of three more There are several digits, each beginning proximally or less regular rows of carpal with a metapodial element (metacarpals on the bones. forelimb, metatarsals on the hindlimb) followed by a The proximal row has a radial chain of phalanges carpal (radiale) at the distal end of the radius, an ulnar The digits rest upon several separate bones, carpal (ulnare) at the end of collectively known as the carpals in the wrist and the ulna and an intermedium the tarsals in the ankle. between the two In some marine vertebrates, the major trend has been toward polyphalangy, a proliferation in the Traditionally, the basic number of phalanges tetrapod limb was thought to consist of five digits that were Species with more than five digits, a condition named and numbered by their known as polydactyly pentadactylous pattern  11/25/2024 Structural modifications of the manus Adaptation for the Life of the Ocean and pes involve reduction in the number of bones, disproportionate The hands have become paddlelike lengthening or shortening of segments, and in some aquatic flippers in well-adapted marine tetrapods, increase in number of amniotes phalanges Flippers are generally flattened and Modern Amphibians: Digits have stout, and in several taxa the been reduced to four or fewer number of phalanges has greatly Birds – three Ungulate (hoofed mammal) – One increased Loss of digits is accompanied by loss or Penguins obtain thrust for swimming reduction of associated carpals and solely from their flipperlike wings, metacarpals or tarsals and metatarsals. their webbed feet serving as rudders. Adaptation for Flight Pes/ Hind foot Two carpals (radiale and ulnare) form in The distal segment of the hind limb of the proximal row, and three in the distal vertebrates, including the tarsus and row. foot As development progresses, the three Comparable bone to bone with the distal carpals unite with the 3 metacarpals manus except there is no consistent to form a rigid carpometacarpus equivalent of the pisiform bone. The first finger of birds that maneuver, In mammals, the fibulare is the alight, and take off in limited spaces is elongated, prominent, and independently specific tarsal that articulates with the movable and is called an alula fibula, but it is more commonly called the calcaneum Bats have five fingers, The thumb is normal and bears a claw The tibiale, commonly called the The other four fingers are elongated and astragalus, actually fuses with the are associated with four greatly elongated intermedium and together they metacarpals articulate with the tibia  11/25/2024 Pes/ Hind foot Tetrapods primitively had four centrale in the pes. The number was reduced to one or two in primitive reptiles and to one in primitive mammals The total structure of the of the anuran pes is provides a suitable base for pushing off when jumping, and is equally useful in locomotion in the water Pes/ Hind foot Pes/ Hind foot Tibiotarsus- united proximal Mammals tarsals and lower end of tibia lack an intratarsal joint but have a Tarsometatarsus - united large hinge joint where the tibia and distal tarsals with the upper end of three fused fibula meet the ankle metatarsals The tibiale (pink) is the principal Most birds have four toes, weight bearing bone of the ankle and a few have three: The other proximal tarsal, the fibulare ostriches alone have two (yellow), is elongated backward in Zygodactyly = with each foot plantigrade, upward in digitirade and having two forward-pointing unguligrades and two backward-pointing toes forming an X  11/25/2024 Adaptations Footedness for Swift- Unguligrade Mammals with pentadactyl Artiodactyls – even toed hands and feet are usually ungulates plantigrade, which means that the weight of the body tended to be distributed the wrists, ankles, and digits all equally between digits 3 rest on the ground and 4. Mammals in which only the first Such a foot is said to be digit has been reduced or lost paraxonic because the tend to be digitigrade, which body weight is borne on means that they bear their two parallel axes. weight on digital arches with Creates a cloven hoof wrist and ankle elevated seen on those animals Unguligrade, few digits touch whose hoof have cleft the floor Ex. Pigs, Camels, Hippos, Ruminates, Antelopes, goat Unguligrade Hominoids Perissodactyls – odd Metatarsal arch, or instep, toed ungulates distributes the body weight the body weight is over four solid bases: the heel increasingly tended to be borne on digit 3, the middle and ball of each foot. digit. This is a mesaxonic foot The great toe, or hallux, is Creates a hoof not opposable in many primates possessing any clefts but not in humans Ex. horse, rhinoceros, zebra, and tapirs  11/25/2024 Three types of ankle joints crurotarsal joint - the ankle joint mesotarsal joint is a simple forms between the crus/shin hinge joint passing between (tibia and fibula) and proximal proximal (astragalus = tibiale) tarsals (astragalus and and (calcaneum = fibulare) and calcaneum) distal tarsal elements the main joint of ankle bending Found in birds between the tibia and the astragalus; the calcaneum has no intratarsal joint - the line of ankle contact with the tibia but forms a flexion passes between the heel to which muscles can attach calcaneum and astragalus mammals Crocodiles