Comparative Anatomy Exam 2

Skeleton

mineralized connective tissue (mostly bone; also dentin, cartilage and enamel/enameloid substances) plus ligaments, tendons and bursa

Bones

matrix of collagen fibers impregnated with hydroxyapatite crystals (calcium, phostphate and hydroxyl ions) from osteoblasts

Water and mucopolysaccharides

cementing subtance which binds the crystals to collagen

Osteon or haversian systems

concentric lamellae around a haversian canal containing an arteriole, venule, lymphatic and nerve fibers

Periosteum

dense fibrous membrane covering all bones except at articular surfaces

Spongy or cancellous bone

trabeculae (tissues) and marrow (reticulum of connective tissue with blood vessels and nerves; adipose and hemopoitietic tissue) interiorly lined with endosteum (thin connective membrane)

Dentin (teeth)

same constituents as dense and spongy bone, forms only in outer layer of dermis and is often coated with enamel

Dentinal tubules

odontoblasts retreat suring its formation and trail protoplasmic processes in canaliculi

Dentin prevalence

found in dermis of early verts, now only present in scales of ganoid/elasmobranch fish and in teeth

Acellular bone

no canaliculi or cell proccesses left after osteoblasts retreat (fibrous sheets of modern fish scales, cementum of vert teeth)

Blastema

aggregation of mesenchyme stimulated to differentiate into another tissue (bone, muscle, cartilage, etc.)

Membrane bone

deposited directly within membranous blastema without cartilaginous stage; no haversian canals

Dermal bone

membrane bone derived from skin dermis

Replacement bone

cartilage formed in advance of ossification and replaced with bone behind= bone growth

Endochondral ossification

deposited where hyaline cartilage already exists

Long bone

begins in the middle of shaft (diaphysis) and grows to both ends (epiphyses); ossification centers also soon appear in each epiphysis (epiphysial plates)

Epiphyses

usually ossify (stop growing) at sexual maturity

Cartilage

consists of sulfated mucopolysaccharides (from chondroblasts) deposited on preexisting collagenous matrix

Hyaline cartilage

least differentiated, precursor of replacement bone, remains only on articular surfaces

Fibrocartilage

thick, dense collagen bundles (intervetebral disks)

Elastic cartilage

contains additional elastic fibers (pinna of ear)

Calcified cartilage

deposition of calcium salts (jaws of sharks)

Homeostasis

hormonally controlled deposition/withdrawal of calcium and other mineral salts from bone in response to dietary intake and cellular demands

Resorption/replacement of bone and cartilage

leads to remodeling of growth demands and used to cope with mechanical stress

Tendons

connect muscles with bone

Ligaments

conect bone to bone

Aponeuroses

flat and very wide tendons and ligaments

Sesamoid cartilages or bones

mineralized tendons and ligaments

Arthrosis

meeting of two bones (joints)

Diarthrosis

freely movable, articular surfaces covered by hyaline cartilage, enclosed in fibrous capsule lined by synovial membrane that secretes a lubricatory fluid (elbow, knee)

Amphiarthrosis

limited movement, unitied by resilient fibrocartilage, fibrous joint capsule without synovial membrane (between vertebral centra)

Synarthrosis

immovable (skull) due to jagged seam (suture) which sometimes is obliterated during development (ankylosis)

Symphysis

bilateral bones immovably joined in body midline by pad or fibrocartilage (pubis)

Mineralized tissues and the invertebrates

matrix is collagen, crystals usually calcium carbonate

Regional components of the skeleton

axial and appendicular skeleton

Axial skeleton

notochord and vetebral column, ribs and sternum, skull and visceral skeleton

Appendicular skeleton

pectoral and pelvic girdles, skeleton of paired fins and limbs, skeleton of median fins of fishes

Heterotropic bones

develop in amniotes in areas of continual stress (human kneecap, steer os cordis, rodent baculum)

Vertebral column (fish)

intervertebral articulations permit only side to side movement

Vertebral column (land invasion of tetrapods)

development of dorsalventral flexibility, some side to side limitation, regional specialization along the column

Modern vertebrae

centrum (notochord in early otogeny), neural arch (snclosing spinal chord), hemal arch or chevron bones (amniotes) in tail (enclosing caudal artery and vein), apophyses (processes) from arches or centrum

Transverse processes (diapophyses)

articulate with ribs, some muscles attach (extend or flex vertebral column)

Pre and postzygapophyses

interlock and limit dorsoventral flexion

Parapophyses

lateral from centra (few tetrapods), articulate with capitulum of bicipital rib (unusual)

Hypapophyses

midventral (snakes)

Morphogenesis of vertebrae

central are developmentally intersegmental relative to the somites and myomeres except in the tail of some fishes and primative tetrapods (two centra per segment, diplospondyly)

The vertebral column of fishes

very divers between species, morphological specializations within a species: dorsal (trunk) and caudal (tail)

Shark vertebral column

notochord through vert column and restricted within centra; centra restricted at each end (amphicelous); vertebral canal (for spinal chord) = paired dorsal plates, dorsal intercalary plates and sometimes supradorsal cartilages; hemal arches = paired ventral plates and sometimes ventral intercalary plates

Fibroelastic ligament

overlies/connects neural spines in ALL fishes

Teleosts vertebral column

well ossified amphicelous vertebrae with remnant of notochord; connected by complex of collagenous and elastic ligaments (facilitate lateral undulation); neural spines often tall; variets of processes from arches and centra (unlike in tetrapods)

Evolution of terapod vertebrae

early tetrapods had amphicelous rachitomous (several bones per segment): hypocentrum, pair of pleurocentra, and a neural arch

Hypocentrum

u-shaped, anterior, cradled notochord

Change to modern amniotes (vertebrae evo)

increased pleurocentra and reduced hypocentra

Change from amphicelous

loss of concavity at one or both ends of centrum

Procelous (anurans, modern novian reptiles)

posterior convex buildup/coalescence of intercentrum (chordal cartilage)

Opisthocelous (salamanders)

anterior convexity

Acelous (mammals)

no concavity, independent fibrocartilaginous intervertebral disc with remnant of notochord (pulpy nucleus)

Reginal specialization in tetrapod columns

Sacral, cervical, thoracic, and lumbar

Sacral

to accept force transmitted through the pelvic girdle

Cervical

for increased mobility of head (more mobile joint with skull, shortened or eliminated ribs, more mobile intervertebral joints (neck)

Thoracic

long ribs restricted to region housing viscera (bony cage, assist external respiration)

Lumbar

between thoracic and sacral

Neck vertebrae (amphibians)

1 → 2 occipital condyles, first cervical vert lacks processes; leads to a dorsoventral rocking of the skull

Neck vertebrae (amniotes)

more cervical vert, first two modified for greater skull movement

Atlas

missing centrum (forms odontoid precess of axis), two superior articular facets meet with occipital condyles (1: reptile, 2: mammals) for ‘yes’, skull and atlas pivot on odontoid process (held in place by transverse atlantal ligament) for ‘no’ (no zygapophyses on atlas)

Heterocelous (birds)

caudal end of centra saddle shaped and accommodated by cephalic end of next vertebra; allows ‘yes’ and ‘no’ movements

Stabilizing the hind limbs

sacrum and synsacrum

Sacrum

ankylosed sacral vertebrae of mammals

Synsacrum (modern birds and armadillos)

ankylosed last thoracic vertebrae, all lumbars, sacrals, some caudals and their ribs, plus the pelvic girdle

Tail vertebrae

urostyle, pygostyle and coccyx

Urostyle (anurans)

from elongated perichordal cartilage at base of larval tail, grows and ossifies after loss of tail at metamorphosis

Pygostyle (birds)

fused caudal vertebrae at end of tail

Coccyx (apes, humans)

fused vestigial caidals

Ribs

formed intersegmentally like the centra vertebrae (by scleroblasts from two successive mesodermal somites)

Fish ribs

basal actinopterigian (Polypterus) and some teleosts have both dorsal ribs (between epaxial and hypaxial muscles) and ventral ribs (develop in myosepta, reach down just external to parietal peritoneum); most fish only have ventral ribs, some (sharks) only have dorsal ribs, some (skates) have none

Tetrapod ribs

most are bicipital with a dorsal head (tuberculum) and a ventral head (capitulum)

Tuberculum

articulates with transverse process

Capitulum

articulation site varies

Two parts of thoracic ribs in amniotes

Costal (adjacent to vertebra), sternal (more ventral, at least some articulate with sternum, may remain cartilaginous as in humans, then called costal cartilages)

Amphibian ribs (anurans and urodeles)

short and ankylosed to transverse processes in anurans

Amphibian ribs (apodans)

long thoughout vertebral column and important for locomotion

Nonavian reptile ribs

'conventional’ in lizards and crocodiles

Nonavian reptile ribs (turtles)

no cervical, those trunk vertebrae fused with costal plates of carapace

Nonavian reptile ribs (snakes)

no sternum, ligamentous connections with scutes (locomotion)

Bird ribs

functional ribs of thoracic basket are thin, flat, and bear uncinate processes; lightweight and sturdy structure for attachment of powerful flight muscles

Mammal ribs

recognizably confined thorax; ‘floating rib’ → costal cartilages (sternal ribs) fail to reach the sternum

Tetrapod sternum

serves as anteroventral site against which pectoral girdles of terrestrial vertebrates can be braced and pectoral flight muscles can be attached

Amphibian sternum

well differentiated only in anurans, consist of several linear segments or cartilage or replacement bone

Reptile sternum

well developed midventral endoskeletal plate (other than in turtles)

Flighted bird sternum

enormous keel or carina for muscle attachment

Terrestrial mammal sternum

Series of bony stenebrae with last segment bearing bony or cartilaginous xiphoid process

Neurocranium

part of skull that 1. protects brain and some sense organs, 2. arises as cartilage (from several centers that expand and unite), 3. usually replaced to some extent by bone

Parachordal

parallel anterior notochord (beneath mid- and hindbrain) → basal plate

Prechordal

anterior or notochord (beneath forebrain → ethmoid plate

Sense capsules

Olfactory, otic, and optic

Olfactory capsule

partially surrounds olfactory epithelium

Otic capsule

completely surrounds otocyst → inner ear

Optic capsule

forms around retina → sclerotic coat of eyeball (not connected to neurocranium)

Unions

ethmoid plate with olfactory capsules, basal plate with otic capsules, both plates complete the floor under the brain

Living agnathans neurocrania

embryonic components remain mostly independent throughout life