THE BONES— FRACTURES 93 



A marked departure from the typical is seen in the first and second 

 members of the series. The atlas is simply a ring of bone from which 

 two plate-like wings project outwards. The edges of the wings project 

 outwards and downwards, and as already remarked, they form a promi- 

 nent landmark in the living animal. Posteriorly the wings present the 

 posterior foramina for the passage of the retrograde arteries. Anteriorly 

 four foramina are seen, two of which, namely, the antero-external, pierce 

 the wings, and give passage to the occipital vessels and the inferior 

 primary divisions of the first spinal nerves. The two remaining 

 foramina, the antero-internal, pierce the ring, and give passage to the 

 first spinal nerves and the cerebro-spinal arteries. Anteriorly the atlas 

 presents two depressed facets for the accommodation of the occipital 

 condyles. The posterior part of the floor of the ring is smooth, and 

 articulates with the odontoid process of the axis. 



The axis has an exceedingly long centrum, from which the odontoid 

 process projects anteriorly. In the horse this process has a very stout 

 base, which has not the marked constriction present in most other 

 animals. The axis has an enormous neural spine, which is thick and 

 powerful, and is bifid posteriorly, where each division terminates on 

 the superior aspect of the posterior oblique process of its side. Its 

 transverse processes are very small. 



Fractures of the wings of the atlas frequently occur, as would 

 naturally be expected from their exposed position. {See Poll-evil.) 

 Fractures of the occipital condyles and the odontoid process are also 

 reported, though the latter are extremely rare, on account of the 

 strength of the process in the horse as already remarked. 



A blow on the side of the neck may ako fracture the tubercle-like 

 extremity of the transverse process, and violent movement of head in a 

 vertical plane may fracture the oblique processes on account of the great 

 pressure thrown upon their articular surfaces. In cases of fracture 

 of the transverse processes prognosis is favourable unless the fracture 

 be across the base, in which case rupture of the vertebral artery 



