170 THE ANATOMY OF THE HORSE. 



following the 7th nerve, and the transverse facial and maxillo-rnuscular 

 vessels, which emerge at the anterior edge of the gland, and the jugular 

 vein, which passes through its substance. In removing the gland, its 

 vessels and nerves must be cut. Its arteries are derived from the 

 external carotid or its collateral branches ; its veins empty themselves 

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

 nerve. 



The deep face 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-styloid, 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 155 and 149 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 arises in common w r ith 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 partly ex- 

 posed 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 by 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 posterior edge of the inferior maxilla. 



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 upper extremity of the styloid (great) cornu 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. 



