Axial Skeleton

Axial Skeleton

The part of the skeleton that includes the vertebral column, ribs, and sternum.

Vertebral Column Functions

Provides structural support, muscle attachment, and protects spinal cord and blood vessels.

Acoelus

Vertebral centra with flat ends, commonly found in most mammals.

Amphicoelus

Vertebral centra that are concave on both ends, found in fish and some amphibians.

Procoelus

Vertebral centra with a concave cranial end and convex caudal end, found in modern reptiles and anurans.

Opisthocoelus

Vertebral centra with a convex cranial end and concave caudal end, seen in salamanders and some mammals.

Heterocoelus

Vertebral centra with saddle-shaped ends, providing extensive movement; found in birds and some turtles.

Intervertebral Bodies

Components in mammals consisting of annulus fibrosis and nucleus pulposus; functions include shock absorption and flexibility.

Sternum

The ventral bone of the rib cage; absent in fish, turtles, snakes, and most amphibians.

Plastron

A structure in turtles that is not a sternum; originates from clavicles, interclavicle, and gastralia.

Keel (Carina)

A modification of the sternum in birds for flight muscle attachment.

Sternebrae

Segmented parts of the mammalian sternum including the manubrium and xiphoid process.

True Ribs

Ribs that articulate directly with the sternum.

False Ribs

Ribs that connect indirectly to the sternum or to each other.

Floating Ribs

Ribs that do not have any ventral articulation.

Costochondral Junction

The junction where the vertebral rib and sternal rib meet.

Tuberculum

The dorsal part of the vertebral rib.

Capitulum

The ventral head of the vertebral rib.

Facet

The articulation point on the vertebra for rib attachment.

Zygopophyses

Interlocking structures in snakes that prevent twisting of the vertebral column.

Urostyle

A fused caudal vertebra in anurans (frogs), aiding in jumping and shock absorption.

Synsacrum

A fused structure in birds combining thoracic, lumbar, sacral, and some caudal vertebrae, providing rigidity for flight.

Pygostyle

Fused terminal caudal vertebrae in birds that support tail feathers and aid in flight maneuvering.

Hemal Spines

Ventral projections on caudal vertebrae in fish, providing protection for blood vessels.

Skeletal Deregionalization

The loss of distinct vertebral regions, commonly seen in snakes.