HEAD AND NECK OF THE HORSE 41 



definite ; but the anterior border blends witli the orbicular muscle of 

 the lip. 



The superficial fibres of the transverse muscle are attached to the 

 laminae of the alar cartilages ; while the deeper fibres are connected 

 with the cornua of the cartilages and the incisive bones. 



M. LATERALIS NASI. — The lateral nasal muscle consists of diffuse, 

 pale fibres springing from the bony boundary of the naso-maxillary 

 notch and ending in the wall of the vestibule of the nose. From the 

 position and direction of its fibres, the muscle may be divided into four 

 parts. (1) The dorsal part consists of fibres arising from the free border 

 of the nasal bone. (2) The posterior part springs from the neighbour- 

 hood of the angle formed by the union of the nasal and incisive bones. 

 (3) The inferior part has origin from the nasal process of the incisive 

 bone. (4) The anterior part consists of a few fibres attached to the 

 concavity of the cornu of the alar cartilage. 



N. INFRAORBITALIS. — The infra-orbital nerve is the terminal branch 

 of the nervus maxillaris (a part of the fifth cerebral nerve) and, in the 

 present dissection, appears at the infra-orbital foramen after having 

 traversed the infra-orbital canal. Immediately on its emergence from 

 the foramen, it divides into three branches. 



(1) The external nasal hrancli (ramus nasalis externus) accompanies 

 the levator labii superioris proprius and divides into two or three 

 branches that supply the wall of the diverticulum of the nostril and the 

 dorsum of the nose. 



(2) The anterior nasal branch (ramus nasalis anterior), larger than 

 the preceding, burrows between the ventral part of the lateral nasal 

 muscle and the nasal process of the incisive bone, to end in the lining 

 of the nostril and the skin of the upper lip. 



(3) The superior labial branch (ramus labialis superioris) is the 



largest of the three divisions of the infra-orbital nerve. It runs 



obliquely downwards and forwards under the naso-labial muscle to reach 



the upper lip, in the skin and mucous membrane of which it ends. 



Delicate filaments are distributed to the tactile- or sinus-hairs of the 



lip. The superior labial branch is connected with the dorsal buccal 



nerve by one or two curved communicating bi'anches, and there is 



frequent union between the branches of the two nerves in the substance 



of the lip. 



Dissection.— 'Exi^ose the surface of the parotid gland by the removal 

 of the inferior auricular muscle, the very thin cutaneous muscle, and the 

 layer of fascia covering the gland. Care must be exercised not to injure 

 the small ramus colli of the' facial (seventh cerebral) nerve, which should 

 be found piercing the gland about its middle. 



