OSTEOLOGY 





partially subdivided by indentations which encroach upon their margins. The 

 inferior articular facets are circular in form, flattened or slightly convex and directed 

 downward and medialward, articulating with the axis, and permitting the rotatory 

 movements of the head. Just below the medial margin of each superior facet is 

 a small tubercle, for the attachment of the transverse atlantal ligament which 

 stretches across the ring of the atlas and divides the vertebral foramen into two 

 unequal parts the anterior or smaller receiving the odontoid process of the axis, 

 the posterior transmitting the medulla spinalis and its membranes. This part 

 of the vertebral canal is of considerable size, much greater than is required for the 

 accommodation of the medulla spinalis, and hence lateral displacement of the 

 atlas may occur without compression of this structure. The transverse processes 

 are large; they project lateralward and downward from the lateral masses, and 

 serve for the attachment of muscles which assist in rotating the head. They 

 are long, and their anterior and posterior tubercles are fused into one mass; the 

 foramen transversarium is directed from below, upward and backward. 



Dens 



Far alar ligaments 



For trans, ligament of atlas 



Superior articular 

 surface 



Foramen 



transversarium 



Spinous process 

 Fid. 87. Second cervical vertebra, or epistropheus, from above. 



Second Cervical Vertebra. The second cervical vertebra (Fig. 87 and 88) is named 

 the epistropheus or axis because it forms the pivot upon which the first vertebra, 

 carrying the head, rotates. The most distinctive characteristic of this bone is 

 the strong odontoid process w r hich rises perpendicularly from the upper surface 

 of the body. The body is deeper in front than behind, and prolonged downward 

 anteriorly so as to overlap the upper and fore part of the third vertebra. It pre- 

 sents in front a median longitudinal ridge, separating tw r o lateral depressions for 

 the attachment of the Longus colli muscles. Its under surface is concave from 

 before backward and covex from side to side. The dens or odontoid process exhibits 

 a slight constriction or neck, where it joins the body. On its anterior surface 

 is an oval or nearly circular facet for articulation with that on the anterior arch 

 of the atlas. On the back of the neck, and frequently extending on to its lateral 

 surfaces, is a shallow groove for the transverse atlantal ligament which retains 

 the process in position. The apex is pointed, and gives attachment to the apical 

 odontoid ligament; below the apex the process is somewhat enlarged, and pre- 

 sents on either side a rough impression for the attachment of the alar ligament; 

 these ligaments connect the process to the occipital bone. The internal structure 



