CER VIC A L VER TEBR^E. 



147 



ment, while in front, immediately behind each superior articular process, is a 

 groove, sometimes converted into a foramen by a delicate bony spiculum which 

 arches backward from the posterior extremity of the superior articular process. 

 These grooves represent the superior intervertebral notches, and are peculiar from 

 being situated behind the articular processes, instead of in front of them, as in 

 the other vertebrae. They serve for the transmission of the vertebral artery, 

 which, ascending through the foramen in the transverse process, winds round the 

 lateral mass in a direction backward and inward. They also transmit the suboc- 

 cipital nerve. On the under surface of the posterior arch, in the same situation, 

 are two other grooves, placed behind the lateral masses, and representing the infe- 

 rior intervertebral notches of other vertebrae. They are much less marked than 

 the superior. The lower border also gives attachment to the posterior atlanto- 

 axial ligament, which connects it with the axis. The lateral masses are the most 

 bulky and solid parts of the atlas, in order to support the weight of the head ; 

 they present two articulating processes above, and two below. The two superior 



Tubercle. 



Diagram of section of odontoid 

 process. 



Diagram of section of 

 transverse ligament. 



Foramen for 

 vertebral artery. 



Groove for rertebral artery 

 and 1st cervical nerve. 



Rudimentary spinoits process.. 



FIG. 110. First cervical vertebra, or atlas. 



are of large size, oval, concave, and approach each other in front, but diverge 

 behind ; they are directed upward, inward, and a little backward, forming a kind 

 of cup for the condyles of the occipital bone, and are admirably adapted to the 

 nodding movements of the head. Not unfrequently they are partially subdivided 

 by a more or less deep indentation which encroaches upon each lateral margin. 

 The inferior articular processes are circular in form, flattened or slightly concave, 

 and directed downward and inward, articulating with the axis, and permitting 

 the rotatory movements. Just below the inner margin of each superior articular 

 surface is a small tubercle, for the attachment of the transverse ligament, which, 

 stretching across the ring of the atlas, divides it into two unequal parts ; the 

 anterior or smaller segment receiving the odontoid process of the axis, the posterior 

 allowing the transmission of the spinal cord and its membranes. This part of 

 the spinal canal is of considerable size, to afford space for the spinal cord ; and 

 hence lateral displacement of the atlas may occur without compression of this 

 structure. The transverse processes are of large size, project directly outward 

 from the lateral masses, and serve for the attachment of special muscles which 

 T in rotating the head. They are long, not bifid, and perforated at their base 

 by a canal for the vertebral artery, which is directed from below, upward and 

 backward. 



The Axis (Fig. Ill) is so named from forming the pivot upon which the first 

 vertebra, carrying the head, rotates. The most distinctive character of this bone 

 is the strong, prominent process, tooth-like in form (hence the name odontoid), 

 which rises perpendicularly from the upper surface of the body. The body is of a 

 triangular form, deeper in front than behind, and prolonged downward anteriorly 

 so as to overlap the upper and fore part of the adjacent vertebra. It presents in 

 front a median longitudinal ridge, separating two lateral depressions for the attach- 



