THE CERVICAL VERTEBRA). 327 
appellation, it has been extended to them. It deviates more completely 
than any of the others from the type of all, the most remarkable differ- 
ences consisting in the almost total absence of body, and in the division 
of the large foramen into two portions by a projecting ridge on the inner 
sideof each lamina. ‘This ridge is not well shown in the fore view of 
this bone (Fig. 13), where it is concealed by the articular surfaces, but 
it is easily seen in Fig. 14. Below it the foramep is occupied by the 
tooth-like (odontoid) process of the second cervical vertebra, which is 
confined in its place by a ligament stretthed across from one ridge to the 
other. Upon this, as on a pivot, the atlas turns, carrying with it the 
head, and allowing of those lateral movements which could not otherwise 
be accomplished. On each side of the spinal foramen are the articular 
surfaces (Fig. 13, 5), which are covered with cartilage, and form a firm 
hinge-like joint between the atlas and the occiput. Still more externally 
are the wings or extended lateral processes (Fig. 13, 2), having a hollow 
Fic. 13.—Fors View oF THE ATLas. 
1. Upper spine. 5. 5. Surfaces for articulation with the condyles 
2. 2. Wings or ale. of the occiput. 
3. Hole for the passage of the spinal cord. 6. 6. Holes for the passage of the vertebral 
4. Lower spine. arteries. 
deeply cut in them, and ending in a small hole through which the ver- 
tebral artery passes on each side to enter the cranium, making a sharp 
convolution in the cavity thas formed for it. The posterior surface shows 
the corresponding margin of the spinal foramen (Fig. 14), of which the 
one part (6) is occupied by the odontoid process, and the other (3) by the 
spinal cord. On each side of this are the articular surfaces, by which it 
Fic. 14.—Backx VIEW OF THE ATLAS. 
1. Upper spine. 5. 5. Surfaces articulating with dentata. 
2. 2. Wings. 6. Surface articulating with the odontsid process 
3. Spinal forame= of the dentata 
4 Lower spine , 
