190 THE ANATOMY OF THE HORSE. 



tlic tensor tympani ; (3) the pterygoid muscles ; (4) the Eustachian 

 tube. 



The Submaxillary Gland (Plates 27 and 31) is, in point of size, the 

 second of the salivary glands. It is elongated, with blunt, rounded extremi- 

 ties ; and it is curved, the concavity being directed upwards and forwards. 

 Its outer surface is related to the tendon of the sterno-maxillaris nuiscle, 

 to the fibrous band connecting that tendon to the mastoid insertion of 

 the mastoido-humeralis, and to the internal pterygoid. The sterno- 

 maxillaris tendon and the above-mentioned fibrous band separate it from 

 the overlying parotid. Its imier surface is related to the guttural 

 pouch, the larynx, and the thyro-hyoid muscle ; and it conceals above 

 the larynx the terminal part of the common carotid artery, and the 

 10th and 11th nerves. Its posterior border is, about its centre, near 

 or in contact with the thyroid gland ; and below that point it is 

 margined by the submaxillary vein. Its anterior border is related 

 above to the stylo-maxillaris muscle, and for the rest of its extent it is 

 traversed by Wharton's duct — the excretory duct of the gland. The 

 superior extremity of the gland is loosely maintained beneath the wing 

 of the atlas ; the inferior extremity is situated within the intermaxillary 

 space, and is crossed o\itwardly by the submaxillary artery. 



Wharton's Duct is formed by the union of small branches which 

 emanate from the gland structure along its anterior border. It descends 

 along that border, and at the lower extremity of the gland it crosses to 

 the inner side of the submaxillary artery, and is continued beneath the 

 tongue, where it will subsequently be followed in its course towards tlic 

 harh. 



The Digastricus (Plate 31). The iipper belly of this muscle has 

 already been seen to arise from tlie styloid process of the occipital bone, 

 where it is confounded witli the stylo-maxillaris muscle. It is succeeded 

 by an intermediate tendon, which plays throiigh a perforation in the 

 tendon of the stylo-hyoid nmscle, in front of which it joins the lower 

 belly. The lower belly has already been dissected in the intermaxillary 

 space, where it is inserte.d by tendinous slips into the posterior border of 

 the inferior maxilla, above the symphysis. 



Action. — To depress the lower jaw. 



The Stylo-hyoid (Plate 31). This nmscle arises from the extreme 

 upper part of the hinder edge of the great cornu. Its inferior tendon is 

 perforated for the passage of the digastricus, and is inserted into the base 

 of the thyroid cornu of the hyoid bone. The external carotid emerges 

 between the belly of the muscle and the great cornu. 



Action, — It carries the base of the tongue and the larynx upwards and 

 backwards, by flexing the joint between the great and small cornua, and 

 the joint between the small cornu and the body. 



Directions. — Pin tlie lower extremity of the submaxillary gland and 



