70 Anatomy oi^ the Rabbit. 



The arch of the vertebra is noteworthy for its projections or processes. 

 On either side is a horizontal plate of bone, the transverse process (pro- 

 cessus transversus), and, dorsally, a median projection, the spinous 

 process (processus spinosus), all three serving for the attachment of the 

 vertebrae to one another by ligaments, and for the attachment of the spinal 

 musculature. Special articular surfaces, borne on low articular pro- 

 cesses (processus articulares), are found on the anterior and posterior 

 margins of the arch. The anterior, or superior articular surfaces are 

 directed for the most part toward the dorsal surface, and are overlapped 

 in the natural condition by the inferior articular surfaces, which are 

 directed toward the ventral surface. A certain amount of movement 

 is permitted bv one surface slipping across the other, the mechanism 

 illustrating the arthrodia, or gliding-joint. 



The cervical vertebrae (vertebrae cervicales) are seven in number. 

 The posterior live are similar, while the anterior two are specially modified 

 in relation to the skull. The posterior vertebrae (Fig. 27, C) are dorso- 

 ventrally compressed, their arches low, and the spinous process short. 

 In the seventh vertebra, however, the spinous process begins to be elon- 

 gated as in the succeeding thoracic vertebrae. In each vertebra the 

 transverse process is perforated by a costo-transverse foramen (foramen 

 transversarium), the latter serving for the passage of the vertebral artery 

 forward to the head. Through the presence of this aperture, the base 

 of the transverse process is divided into two parts, namely, a dorsal, 

 or posterior root (radix posterior), and a ventral, or anterior root (radix 

 anterior). The anterior root is a coalesced rib, and is comparable in its 

 general relations to the normal ribs of the thoracic vertebrae. 



The first vertebra is the atlas (Fig. 21, A). It is peculiar in lacking 

 the vertebral body, the latter being represented by the odontoid process 

 of the epistropheus (cf. Plate II) ; also in possessing special articular 

 surfaces, and in having its transverse process greatly flattened in the 

 dorsoventral direction. It consists of a ventral half-ring, the anterior 

 arch (arcus anterior), a dorsal half-ring, the posterior arch (arcus pos- 

 terior), with paired lateral masses (massae laterales) uniting them. 

 The lateral masses also form the bases of the transverse processes. The 

 anterior arch bears on its ventral side a small backwardly-directed 

 process, the anterior tubercle (tuberculum anterius). A similar 

 posterior tubercle (tuberculum posterius) on the dorsal surface of the 

 posterior arch is comparable to the spinous process of an ordinary 

 vertebra. The anterior surface of the atlas bears on either side an 

 extensive concave smooth surface, the superior articular pit (fovea 

 articularis superior), for articulation with the convex occipital condyles 

 of the skull. Its posterior surface bears on either side a somewhat 

 triangular inferior articular facet (facies articularis inferior) for articula- 

 tion with the epistropheus. These surfaces take the place of the arch- 

 articulations of ordinary vertebrae. Through the compression of the 

 transverse process, the costotransverse foramen is converted into a 

 canal. The anterior aperture of this leads by a shallow groove, the 

 sulcus arteriae vertebralis, into a second aperture perforating the 

 posterior arch. 



