254 



THE HORSE. 



brain, the division into separate pieces being far more secure than 

 if the whole were in one. 



The bones of the face, including the lower jaw and os 

 liyoides, depend from the neural arch or brain-case much in the 

 same way as the ribs and pelvic bones posterior to them are at- 

 tached to the vertebrae, and though they enclose organs of less vital 

 importance, yet they are perfectly analogous to these parts in their 

 types and in the offices which they perform. 



OF THE THOllACIC ARCH AND ANTERIOR EXTREMITIES. 



Lying in the horse at some distance posteriorly to the 

 three first segments of the hsemal arch (the bones of the face, lower 

 jaw, and os hyoides), and separated from them by the neck, where 

 there is a hiatus, the thoracic arch and anterior extremities de- 

 pend from the vertebrae corresponding to them. In many of the 

 higher vertebrates the fore extremity is firmly united by a joint 

 to the thorax, and may be considered with it ; but in the horse it 

 is only attached by muscles, the thorax being slung between the 

 upper edges of the blade-bones by means of two broad sheets of 

 muscular fibres. Hence the collar-bone is entirely absent in this 

 animal ; and thus, while he is free from dislocations and fractures 

 of that bone, to which he would be constantly subject if it were 

 present, he is rendered more liable to strains and rheumatic in- 

 flammations of the muscular sling, by which freedom of action is 

 impaired. 



