THE SKELETON IN MAMMALIA. VERTEBRAL COLUMN. 445 



enclose between them a wide space. These processes are not 

 completely ossified till the animal is adult. 



In all UNGULATA the number of cervical vertebrae is seven. 

 Among the Artiodactyla two forms of the odontoid process of 

 the axis occurs ; in the Suina and Tragulina it is conical, in 

 the Ruminantia and Tylopoda it is spout-like (fig. 88, 4). The 

 atlas in the Suina and to a less extent in the Ruminantia has 



B fe.- 



FIG. 88. 



A 



ATLAS (B) AND AXIS (A) VEBTEBRAE OF AN Ox (Bos 

 taurus) x %. (Camb. Mus. ) 



8. 



7. 



anterior opening of the verte- 



brarterial canal, 

 foramen for the exit of the 



second spinal nerve, 

 neural spine, 

 postzygapophysis. 



1. neural canal. 



2. transverse process. 



3. surfaces for articulation with 



the occipital condyles of 

 the skull. 



4. spout-like odontoid process. 



5. hypapophysis. 



long flattened transverse processes, and the remaining cervical 

 vertebrae are opisthocoelous. Those of the Giraffe and Llama 

 (fig. 103) are noticeable for their great length. In the Tylo- 

 poda the posterior half of the vertebrarterial canal is confluent 

 with the neural canal. 



The Perissodactyla have remarkably opisthocoelous cervical 

 vertebrae. Those of Macrauchenia have the posterior half of 

 the vertebrarterial canal confluent with the neural canal as in 

 Tylopoda. In the Proboscidea they are short flattened discs 

 slightly opisthocoelous ; the axis and seventh vertebra and to 

 a less extent the sixth have high neural spines. 



