4.1 - axial skeleton

neural arch

positioned mid-dorsally, surrounds the nerve tube

neural spine

projects dorsally from neural arch

centrum

spool-shaped body surrounding notochord

hemal arch

projects ventrally from centrum only in caudal vertebrae (to protect blood vessels)

hemal spine

extends ventrally from hemal arch

amphicoelus

• both ends concave

• sharks, teleosts, extant amphibians

acoelus (amphiplatyan)

• both ends flat

• some mammals

heterocoelus

• both ends saddle-shaped

• necks of turtles and birds

opisthocoelus

• anterior convex

• posterior concave

• soma mammals

procoelus

• anterior concave

• posterior convex

basapophyses

• paired vertebral processes on centrum (likely remnants of hemal arch bases now articulation with ventral rib or remaining hemal arch)

diapophysis and parapophysis

lateral projections from the centrum that articulate with dorsal (tuberculum) and ventral (capitulum) heads of dorsal rib

heteropophysis

unpaired midventral processes from centra

zygapophysis

articulations between successive vertebrae

red

zygaopohyses

blue

post-zygapophyses

green

pre-zygapophyses

synsacrum

most of the posterior thoracic elements fuse with all the lumbar, sacral, and some caudal

pygostyle

formed when the last few caudal elements fuse

1

transverse process

2

postzygapophysis

3

neural arch

4

neural spine

5

neural canal

6

prezygapophysis

7

transverse foramen

8

centrum

1

neural spine

2

prezygapophysis

3

transverse process

4

neural canal

5

centrum

6

demifacet

7

full facet

8

neural arch

9

postzygapophysis

1

accessory process

2

postzygapophysis

3

neural spine

4

mammillary process

5

prezygapophysis

6

centrum

7

transverse process

1

centrum

2

hemal arch

1

articular surface with ilium

2

intervertebral foramen

3

postzygapophysis

4

neural spine

5

prezygapophysis

6

centrum

C1

• atlas

• greatly reduced centrum/anterior arch

• largest neural canal

• no neural spine

• broad superior articulations for joints with skull

• facet for dens on the dorsal surface of anterior arch

• transverse process are short and have large foramen

atlas

C2

• axis

• blunt bifid neural spine

• broad zygapophysis for articulation with atlas

• odontoid process/dens projects cranially

axis

primary curvature

• thoracic, sacral

• kyphoses

secondary curvatures

• lumbar, cervical

• lordoses

cervical

• large neural canals

• bifid spinous processes for attachment of nuchal ligament

thoracic

• heart shaped body

• round neural arch

• sharply sloping neural spine

lumbar

• blunt, dorsally pointing neural spines (hatchet-like)

• no additional processes

• bodies are shorter but broader

• laterally extending transverse processes

sacral

• large lateral masses

• broad regions for the joints formed with the ilium (sacroiliac joint)

• anterior and posterior foramen for the spinal nerves

caudal

• fused into coccyx bone

• progressively smaller

• loss of neural canal