Fins limbs and vertebral column

most possess two dorsal fins-- one anterior (behind the head) and one posterior (in front of the tail)

composed of basal cartilage

Caudal fin in primitive chondrichthyes was externally symmetrical (despite asymmetrical internal skeleton)

• show variation among the classes of organisms
• - within derived chondrichthyes, fin muscles are present believed to help generate lift and movement
• - they articulate with pectoral/ pelvic girdle via basal cartilages--> propterygium, mesopterygium, metapterygium

Fins are webs of skin supported by horny spines

contain dorsal fin, fin rays, anal fin, ventral fin, and a caudal fin

• Only one species of lobe-finned fish still exists: Coelacanth
• contain fleshy, lobed, paired fins
• pelvic and pectoral fins resemble tetrapod limbs, which are believed to have evolved from these fins

- all have four limbs except the legless caecilians and some salamanders

- regenerative capabilities after injury or amputation of limbs

- bones are fully ossified with no cartilage reminisces at maturity: shaft (diaphysis) of the bone takes up most of the length, ends of bones become epiphysis after ossifying-- allows for growth zones for cartilage around ossification centers between epiphysis and diaphysis

• differ from mammals in that the wrist has three rows of carpal bones
• -- Proximal: radial, ulnar, intermedium, pisiform
• -- Middle: three central carpals
• -- Distal: 5 distal carpals
• -- Plantigrade (all bones of manus on the ground)

• - appendicular skeleton includes flippers and hind limbs
• - same long bones as mammals
• - similar carpals and tarsals to mammals in flippers

four limbs similar to crocodiles

• lack paired limbs (snakes)
• lizards similar to other orders

adaptive modifications of manus

• - birds: loss of digits and bones plus fusion of some bones
• - bats: 5 digits, elongated metacarpals with phalanges to support the patagium
• - pterosaurs-- 4th digit elongated to support patagium

membranous structure that aids an animal in gliding or flying

plantigrade

digigrade

ungiligrade

monkeys, apes, humans

• flat footed
• all bones of manus on the ground
• opposable thumbs--> saddle joint at base of thumb where it meets palm

rabbits, rodents

• 1st digit is reduced or lost
• manus and pes are elevated

• reduced number of digits
• walk on tips of remaining digits
• claws become hooves

pleurocentrem and intercentrum are fused

resembles the vertebral body of most mammals

• vertebral arch surrounds teh spinal cord
• under arch is pleurocentrum, which protects the notochord
• under pleurocentrum is intercentrum, also protects notochord

• cylindrical piece of bone below the vertebral arch
• no trace of separate elements present in early tetrapods

• highly variable number of vertebrae
• - several hundred can exist in a snake
• contain haemal arches that attach below the base of the spine
• often contain primitive intercentra
• --> small crescent shaped bony elements lying between adjacent vertebrae
• anterior surface of spinal cord has a concave socket. 
• --> expanded convex face of the next vertebrae sits

• variable number of cervical vertebrae: allows for only true flexibility of bird
• Thoracic vertebrae almostalways partly fused: provides brace for wings during flight
• sacral are fused with lumbar vertebrae: can also contain some caudal and thoracic fused vertebrae; this fusion creates the synsacrum

cervical vertebrae (most superior): contain transverse foramina

thoracic (inferior to cervical): contains costal fossa

Lumbar (inferior to thoracic)

Sacrum (inferior to lumbar)

Typical vertebrae contain: superior/ inferior articulate fossa, spinous process, transverse process, lamina, pedicle, vertebral foramen, vertebral arch, and centrum