156 DISSECTION OF THE DOG 



piece of cartilage (cartilago palpebral tertise) which will be examined along with 

 tlie other contents of the orbit. 



Dissection. — Remove the skin from the face and proceed to examine the 

 underlying muscles. The nerves and vessels of the face must be carefully 

 preserved. 



M. zygomaticus. — A narrow, band-like muscle arising from the seutiform 

 cartilage of the ear, the zygomatic crosses the face obliquely and is inserted 

 at the angle of the mouth. 



M. risorius. — The risorius muscle is merely that portion of the cutaneous 

 muscle of the face which lies in the region of the angle of the mouth and is 

 inserted close to the termination of the zygomatic muscle. 



M. quadratus labii superioris. — Covering the side of the nose, the 

 quadrate muscle is divisible into three parts : (1) 31. nasolabialis, with fibres 

 arising from the maxillary and frontal bones in the neighbourhood of the medial 

 commissure of the eye, and from the frontal fascia, to end in the substance of 

 the upper lip ; (2) m. malaris, thin and connected with the foregoing at its 

 origin, where it blends also with the orbicular muscle of the eye, and confused 

 with the buccinator muscle at its insertion ; (3) m. levator labii superioris 

 proprius, with an origin from the maxillary bone in the region of the infra- 

 orbital foramen, and an insertion about the nostril. 



M. caninus. — Ventral to the proper levator of the upper lip in position, 

 the canine muscle arises close to the infraorbital foramen and from the canine 

 fossa of the maxillary bone. Its insertion is into the upper lip. 



M. buccinator. — The buccinator muscle consists of two strata : (1) The 

 more superficial stratum contains fibres running obliquely from the alveolar 

 border of the maxilla to the lateral face of the mandible ; (2) the deeper fibres 

 run obliquely downwards and forwards from the maxilla on a level with the last 

 two or three cheek-teeth to the lateral face of the mandible. 



M. orbicularis oris.— A sphincter muscle contained in the lips, the 

 orbicular muscle of the mouth, provides a means by which the lips are 

 approximated and the entrance to the mouth is closed. 



Mm. ixcisivi labii superioris et inferioris. — The upper and lower 

 incisive muscles are best demonstrated by removing the mucous membrane 

 from the inside of the lips. In dissecting the upper incisive muscle of each side 

 a large branch of the infraorbital nerve is exposed. 



The muscles consist of bundles of fibres passing into the lips from the 

 incisive bone and the mandible on a level with the second and third incisor 

 and the canine teeth. 



M. m \ssi;ter. — The masseter muscle is powerful and lies over the mandible 

 ventral to tin- zygomatic arch. A complete examination should be postponed. 



Glandula parotis. — The parotid gland of the dog is relatively small. 



