Fig. 8.--Caudal Vertebra, from near the caudal end of the tail.
Fig. 9.--Fourth Caudal Vertebra, ventral view. _a_, transverse processes; _b_, cranial articular processes; _c_, hæmal processes; _d_, chevron bone.]
The parts of a typical vertebra--vertebral arch, transverse processes, cranial and caudal articular processes--may be recognized in the vertebræ as far back as the eighth or ninth. The transverse processes (Fig. 9, _a_) are directed caudad and decrease rapidly in length. They are very small on the ninth vertebra, but may be recognized for a considerable distance back of this. The spinous process disappears at about the fourth caudal vertebra, and the vertebral canal becomes gradually smaller caudad, until on the eighth or ninth vertebra it becomes merely a groove open dorsad.
Caudad of the third vertebra for a considerable distance, each centrum bears on each lateral face at its cranial end a short =anterior transverse= process, and on its ventral face at its cranial end a pair of rounded tubercles, =hæmal processes= (_c_), which articulate with a small pyramidal =chevron= bone (_d_) so as to enclose a canal. These structures disappear caudad.
=Cervical Vertebræ.= =Vertebræ cervicales= (Fig. 10).--The cervical vertebræ number seven. The first two of these are so peculiar as to require a separate description, so that the last five may be first considered.
Passing craniad from the fourth thoracic vertebra to the third cervical there is a gradual transition. The centra of the cervical vertebræ are broader and thinner than those of the thoracic vertebræ, while the vertebral arches and vertebral canal are larger (Fig. 11). The caudal end of each centrum is concave and looks dorsocaudad when the centrum is held with its long axis horizontal. The cranial end of the centrum is convex and looks ventrocraniad when the centrum is horizontal. These peculiarities are more marked in the third vertebra than in the seventh. The spinous processes grow rapidly shorter as we pass craniad; the fifth, sixth, and seventh are directed dorsocraniad, the third and fourth dorsad.
[Illustration: FIG. 10.--CERVICAL VERTEBRÆ, SIDE VIEW.
_a_, spinous processes; _b_, cranial articular processes; _c_, caudal articular facet; _d_, intervertebral foramina; _e_, transverse process proper; _f_, processus costarius; _g_, wing of the atlas; _h_, dorsal arch of the atlas; _i_, atlantal foramen.]