166 



THE ANATOMY OF THE HOR«E. 



iuto the jugular or auricular veins ; its nerves come from the 7th cranial 

 nerve. 



The deep ftice of the parotid gland is related to the following 

 structures : — The mastoid insertion of the mastoido-humeralis, the ter- 

 minal tendon of the sterno-maxillaris, the stylo-maxillaris, the digas- 

 tricus (upper belly), the occipito-stjloid, the stylo-hyoid, the submax- 

 illary gland, the great cornu of the hyoid bone, the guttural pouch, the 

 external carotid artery (with its terminal, and some of its collateral, 

 branches), the initial part of the jugular vein (formed by the junction of 

 the superficial temporal and internal maxillary veins), and the 7th 

 nerve. 



The Tendons of the Mastoido-Humeralis and Sterno-Maxillaris. 

 These muscles are described at pages 152 and 145 respectively. The 

 two tendons are connected by a fibrous expansion, which is included 

 between the parotid and submaxillary glands. When they have been 

 examined, the fibrous expansion and the tendon of the sterno-maxillaris 

 may be removed. 



The Stylo-Maxillaris. This muscle is not distinct from the digas- 

 tricus (upper belly). It anses in common with that muscle from the 

 styloid process of the occipital bone, and it is inserted into the angle of 

 the jaw. 



Action. — To depress the lower jaw, and assist in opening the mouth. 



The DiGASTRicus (Plate 31). This muscle will be only imperfectly 

 exposed at present. It consists of an upper and a lower muscular belly, 

 with an intermediate tendon. The lower belly will be met in the dis- 

 section of the intermaxillary space ; and the tendon, in the dissection for 

 the exposure of the mouth and pharynx. The upper belly arises from 

 the styloid process of the occipital bone, in front of the origin of the 

 preceding muscle, with which it is confounded. It is succeeded b}- the 

 intermediate tendon, which plays through a perforation in the tendon of 

 the stylo-hyoid, and is continued by the lower belly. The latter becomes 

 inserted into the edge of the inferior maxilla, behind the symphysis. 



Action. — To depress the lower jaw and open the mouth. 



The Occipito-Styloid (Plates 31 and 32). This muscle arises from 

 the front of the styloid process of the occipital bone ; and it is inserted 

 into the extremity of the styloid (great) coi-nu of the hyoid bone, behind 

 its point of articulation with the skull. The deep face of the muscle is 

 lined by the mucous membrane of the guttural pouch ; and in the 

 operation for opening the pouch, the muscle is perforated. 



Action. — To flex the temporo-hyoideal joint, and carry backwards the 

 hyoid bone and the parts attached to it. 



The Stylo-Hyoid (Plate 31). Only the origin of this muscle, from the 

 heel-like part of the great cornu, will at present be seen. It should be 

 identified, and preserved for examination at a later stage. 



