

THE RABBIT. 



69 



0*V>M. 



Fig. 81. ATLAS. 

 Front view. 



arteries (each a branch of the subclavian of its side) are 

 enclosed in them. A study of the development of these 

 bones shows that the part ventro-lateral to this canal 

 ossifies separately from the rest of the transverse process ; 

 and the form of the 

 equivalent structures in 

 certain peculiar lower 

 mammals and in reptiles 

 leaves no doubt that this 

 part is really an ab- 

 breviated rib, fused up 

 with the transverse pro- 

 cess and body. 



The two anterior cer- 

 vical vertebrae are peculiar. *The first is called the atlas 

 (fig. 31) : it has great articular faces for the condyles 

 ( 15) of the skull, a deficient centrum, no zygapophyses, 

 and very large transverse processes. The next is the 

 axis (fig. 32), and it is distinguished by an odontoid peg, 

 which fits into the space where the body of the atlas is 

 deficient. In development the centrum of the axis ossifies 

 from one centre, and the odontoid peg from another, which 

 at that time occupies the position of centrum of the atlas. 



So that it would 

 seem that the atlas 

 is a vertebra minus 

 a centrum, and the 

 axis is a vertebra 

 plus a centrum, 

 added at the ex- 

 pense of the atlas. 

 The axis has a 

 strong, ridge-lik* 

 neural spine, pos- 

 terior zygapophyses 



only, and its transverse processes are only recognizable 

 as such through the presence of the vertebrarterial canal. 

 The articulations between axis and atlas and between atlas 

 and skull are synovial, intervertebral pads being wanting. 

 This, along with the absence of zygapophyses, results in a 



Fig. 32. Axis. 

 Side and front views. 



