The; Vertebral Column. 71 



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 liga- 

 ment 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 (Fig. 27, 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 trans- 

 verse 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. 27, DJ. 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 vertebrae 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 are, on the whole, slightly 

 increased in extent. The anterior ten are directed backward, the elev- 

 enth is almost vertical, while the twelfth is directed forward, like those 

 of the succeeding lumbar vertebrae. 



The lumbar vertebrae (vertebrae lumbales) are seven in number. 

 They are large vertebrae, conspicuous for their extensive surfaces and 

 processes for muscular attachment (Fig. 27, E, F). The transverse 

 processes continue the general line of the ribs of the thoracic region. 

 They are directed forward, as well as outward, and the tip of each is 

 formed by a thin triangular plate (processus triangularis), which represents 

 a fused rib. At the posterior side of the base of each is a short, flattened 

 projection, the accessory process (processus accessorius). The spinous 

 process is especially well-developed, and is directed forward. The 

 articular processes are rotated upward, so that their surfaces are directed 



