368 



THE ANATOMY OF THE HORSE 



Still more externally are the wings or extended lateral processes (Fig. 1 3, ,,), 

 having a hollow deeply cut in them, and ending in a small hole through 

 which the vertebral artery passes on each side to enter the cranium, making 

 a sharp convolution in the cavity thus formed for it. The posterior surface 



Fia. 14. — Back View of the Atlas. 



1. Upper spine. 



2. 2. Wings. 



3. Spinal foramen. 



4. Lower spine. 



5. 5. Surfaces articulating with dentata. 



6. Surface articulating with the odontoid process 



of the dentata. 



shows the corresponding margin of the spinal foramen (Fig. 14), of which the 

 one part (6) is occupied by the odontoid process, and the other (3) by the 

 spinal cord. On each side of this are the articular surfaces, by which it is 

 attached to the corresponding surfaces of the second vertebra, and still 

 more externally are the alse or wings. The superior and inferior spinous 

 processes are shown at 1 and 4 in each engraving. 



Fig. 15.— Anterior View of the Second Vertebra, called Dentata or Axis. 



1. Superior spine. 



2. 2. Transverse processes. 



3. 3. Surfaces articulating with corresponding ones 



on tlie posterior part of the atlas. 



4. Odontoid process. 



5. Inferior siiine. 



6. S])inal foramen. 



7. 7. Foramina for the passage of the vertebral 



arteries. 



The second cervical vertebra, called axis from its being the centre 

 on which the atlas turns, and dentata, from its presenting a tooth-like 

 process for this pui-pose, approximates somewhat more nearly to the usual 

 type, but is remarkable for the process already alluded to, which is shown 

 at 4^ Fig. 15. Inferiorly this part is smoothly I'ounded, to enable it to 

 play against the first vertebra, while superiorly it is flatter, and is in 



