The pectoral girdle lies external to the ribs, and has no bony attachment to the axial skeleton.
The axial skeleton is generally long, and that of the limbs frequently comparatively short, or sometimes absent.
This exoskeleton differs from the main or axial skeleton of the higher animals, the latter being inside of the body.
The cranium is a compact bony box, forming the anterior expanded portion of the axial skeleton.
The axial skeleton includes the vertebral column, the ribs, and the skull.
The commencing formation of the cells which form the axial skeleton from the inner (splanchnopleuric) layer of the muscle-plate.
In birds we distinguish between the following regions of the axial skeleton.
For further description of the axial skeleton, see Hibbard .
axial skeleton n.
The bones of the head and trunk, excluding the pectoral and pelvic girdles.