160 ANATOMY OF THE RABBIT 



articulations of ordinary vertebrae. As a result of the flattening 

 of the transverse process, the costo-transverse foramen is extended 

 into a tubular canal. The anterior aperture of this is connected by 

 a shallow groove, the sulcus arteriae vertebralis, with a foramen 

 perforating the posterior arch (foramen obliquum). Through this 

 latter foramen, represented in some mammals by separate alar and 

 intervertebral foramina, the vertebral artery and the first cervical 

 nerve enter the vertebral canal. 



The space enclosed by the atlas is divided into a dorsal portion, 

 corresponding to the vertebral foramen of other vertebrae, and a 

 ventral portion which in the natural condition lodges the odontoid 

 process of the epistropheus. The division is effected partly by a 

 small tubercle on the inner side of each lateral mass, and partly 

 by a transverse ligament which is stretched between these tubercles 

 and over the dorsal surface of the odontoid process. On the floor 

 of the ventral portion, a rounded articular surface, the fovea 

 dentis, marks the point of articulation of the anterior articular facet 

 of the odontoid process with the inner surface of the anterior arch. 



Epistropheus 



The second vertebra is the epistropheus or axis (Fig. 82, B). 

 It resembles the succeeding cervical vertebrae more closely than 

 does the atlas. It is noteworthy for its great size, for the lateral 

 compression of its arch and spinous process, and for the possession 

 of a stout forwardly-directed odontoid process, or tooth (dens 

 epistrophei). It is articulated with the atlas through an anterior 

 articular facet, borne on the ventral surface of the odontoid process, 

 and by large paired superior articular facets borne on its base. The 

 spinous process of this vertebra and the transverse processes of the 

 atlas are three main points of attachment for the occipital muscu- 

 lature, which passes between the head and neck. 



Consideration of the form and relations of the articular surfaces 

 will make it evident that the articulation between skull and atlas 

 provides chiefly for a nodding movement and that that between 

 atlas and epistropheus allows mainly a pivoting movement of the 

 head. Simple bending of the head to one side or the other is the 

 main movement permitted between the remaining cervical verte- 

 brae, in which the superior and inferior articular surfaces respec- 

 tively face mainly dorsad and ventrad. 



