MYOLOGY 159 



ridge, which is sometimes very pronounced, which the 

 transverse processes of the atlas make on each side of this 

 part of the neck. 



In the dog and the cat, the superior and anterior region 

 of the neck is thick and of rounded form, on account of the 

 development which the splenius presents in those animals ; 

 but it is covered by the mastoido-humeral. 



This latter relation is also found in the ox, but the splenius 

 in this case is but slightly developed. 



When the splenius contracts it extends the head and neck,, 

 while inclining them to its own side. 



If the splenius of one side contracts at the same time as 

 that of the opposite, the extension takes place in a direct 

 manner — that is to say, without any modifying lateral 

 movement. 



Infrahyoid Muscles 



Having studied the lateral surfaces of the neck, we must 

 now examine the anterior part of this region. Here, between 

 the two sterno-mastoid muscles, we find a space broader 

 above than below, in which are situated the larynx and the 

 trachea, to the general arrangement of which is due the 

 cylindrical form which this region presents. This space 

 corresponds to that which in the neck of man is limited 

 laterally by the sterno-cleido-mastoid muscles, below by 

 the fourchette of the sternum, and above by the hyoid 

 bone. In animals, as in man, it is called the infrahyoid 

 region. 



The hyoid bone in quadrupeds is situated between the two 

 rami or branches of the lower jaw. Owing to this disposi- 

 tion, the region above this bone, instead of having its surface 

 projecting a little beyond the inferior border of the maxillary 

 bone, is depressed. This is especially so in the horse. It 

 is there that we find in this animal the region known as the 

 trough {auge) ; the larynx corresponds to that part known as 

 the gullet. 



The muscles which occupy the infrahyoid region are : the 

 sterno-thyroid, the sterno-hyoid, and the omo-hyoid. There 



