176 THE ANATOMY OF THE HORSE. 



The DiGASTBicus. This muscle is named from its having two fleshy 

 bellies, with an intermediate tendon. The upper belly arises from the 

 styloid process of the occipital bone, being confounded with the stylo- 

 maxillaris. It is succeeded by the intermediate tendon, which plays 

 through the tendon of the stylo-hyoid muscle ; but this and the upper 

 belly are at present concealed within the jaw. The lower belly is placed 

 in the intermaxillary space, where it is partly covered by the lymphatic 

 glands, and is related anteriorly to the mylo-hyoid muscle. It is inserted 

 by a flat fasciculated tendon into the posterior edge of the horizontal 

 ramus, a little distance above the symphysis. 



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



The Mtlo-hyoid Muscles stretch across the intermaxillary space, and 

 form a support for the tongue. Each muscle arises from a line on the 

 inner surface of the horizontal ramus behind its alveolar border ; and its 

 fibres pass transversely inwards, the most superior getting inserted into 

 the body and glossal process of the hyoid bone, and the others into a 

 median fibrous raphe between the two muscles. The muscle is to be 

 left intact at present, and its attachments will be better seen in the 

 dissection of the mouth. 



Action. — To raise the body of the tongue towards the roof of the 

 mouth, and thus assist in mastication and deglutition. 



Nerve to the mylo-hyoid and inferior belly of the digastric. This 

 is a branch of the inferior maxillary division of the 5th cranial nerve. 

 It descends between the internal pterygoid muscle and the vertical 

 ramus ; and, passing above the upper edge of the mylo-hyoid, it runs 

 downwards on the surface of that muscle, in company with the sub- 

 mental artery. In part of its course it is covered by the lower belly of 

 the digastricus, and it sends to that muscle a distinct branch, which 

 enters it on its outer side. 



THE APPENDAGES OP THE EYE. 



These are — the eyelids, the membrana nictitans, the caruncula 

 lachrymalis, the conjunctival membrane, and the lachrymal apparatus. 

 The lachrymal gland — the most important part of the last mentioned 

 apparatus — will be dissected with the interior of the orbit ; but the 

 other structures enumerated are to be examined now. 



The Eyelids. The front of the eye is protected by two movable cur- 

 tains — the upper and lower eyelids ; and at the inner side of the eye there 

 is placed another structure — the membrana nictitans, which plays the 

 part of a third eyelid. The upper lid is larger than the lower, and has 

 a greater range of movement. Each eyelid presents two surfaces, two 

 borders, and two extremities. The outer or facial surface is formed by 

 a continuation of the skin, and is covered by short hairs. Among these 



