22 ANATOMY OF THE RABBIT. 
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 them 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. 
The second vertebra is the epistropheus or axis (Fig. 56, 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 form together three main points of attach- 
ment for the occipital musculature. 
The thoracic vertebrae (vertebrae thoracales) are twelve in 
number. They are distinguished chiefly by the possession of 
articular pits for the attachment of ribs (Fig. 56, D). A rib is 
articulated at two points, namely, one on the body of the vertebra, 
the other on the transverse process. The former is marked by a 
small round depression, the costal pit (fovea costalis), or costal 
facet. In the last two vertebrae the facet is borne wholly on the 
vertebral body to which the rib belongs. In the remaining verte- 
brae a complete articulating surface is formed by two demifacets, 
one being on the vertebra to which the rib belongs, the other on the 
vertebra immediately in front. The articulation of a rib-with a 
transverse process is marked by an oval facet, the costal pit of the 
transverse process (fovea costalis transversalis). It is present 
only in the first ten of the thoracic vertebrae. 
In all vertebrae of the thoracic series the spinous processes are 
well-developed. They increase in length to the third, and then 
become gradually shorter, although their surfaces, on the whole, are’ 
slightly increased in extent. The anterior ten are directed back- 
ward, the eleventh is almost vertical, while the twelfth is directed 
forward, like those of the succeeding lumbar vertebrae. 
