Page:Structure and functions of the body; a hand-book of anatomy and physiology for nurses and others desiring a practical knowledge of the subject (IA structurefunctio00fiskrich).pdf/96

• bræ join to form the intervertebral foramen for the outward

passage of nerves and the inward passage of blood-vessels.

The distinguishing mark of the cervical vertebræ is the foramen in each transverse process, through which the vertebral arteries run to the skull. They are also smaller than the dorsal and lumbar vertebræ. The dorsal vertebræ are distinguished by having on the transverse processes and on the body smooth articular surfaces called facets and demi-facets for articulation with the ribs. The lumbar vertebræ are the largest and heaviest and have the thickest spine. By the time the sacral region is reached, however, the vertebræ have only a rudimentary spinous process. Moreover, in adult age the sacral bones grow together and form one triangular bone, the sacrum, which has a broad base called the promontory of the sacrum and a blunt apex. It is concave in front and convex behind and has an articulating surface for joining the pelvic bones. In the case of the coccyx also the four original bones, all rudimentary in character and supposed to be the survival of a tail, grow together to form one bone. Together the sacrum and coccyx form the posterior wall of the true pelvis.

Fig. 33.—The sacrum, from before. (Drawn by D. Gunn.)