HEAD AND NECK OF THE HORSE 55 



Within the substance of the tongue it communicates with the lingual 

 vein. 



It should be noted that the dorsal lingual vein is not the com- 

 panion of any artery. 



(2) V. alveolaris inferior. — The inferior alveolar vein lies within 

 the mandibular canal, and joins the internal maxillary immediately 

 on its exit from the mandibular foramen. 



(3) V. temporalis profunda. — The deep temporal vein begins in 

 the temporal fossa and gains the internal maxillary by crossing in 

 front of the mandibular joint. 



(4) Rami pterijgoidei from the internal pterygoid muscle. 



The vessels that join the second part of the internal maxillary 

 vein are the superficial temporal, posterior auricular, masseteric, 

 parotidean rami, inferior cerebral, and occipital, which have pre- 

 viously been examined (page 43). 



The cheeks (buccie). — This is a convenient stage at which to 

 complete the examination of the cheeks. The lips, however, should not 

 be further dissected at the present time. 



The cheeks form the lateral boundaries of the mouth, and extend 

 backwards from the region of the commissure of the lips. Their upper 

 and lower borders are attached to the maxilla and mandible close to the 

 alveolar margins of these bones. 



Three layers can be distinguished in the cheek. (1) The outermost 

 of these consists of thin and very pliable skin. (2) The middle layer 

 contains the buccal glands, of which the dorsal group was examined 

 earlier (page 51), and certain muscles. Though the buccinator is the 

 main muscle of the cheek, parts of the risorius, zygomaticus, nasolabialis, 

 caninus, and depressor labii inferioris are included. Of the muscles 

 there only remains to note the origin of the buccinator (molar part) and 

 the depressor of the lower lip from the maxillary tuber and the coronoid 

 process of the mandible. (3) The mucous membrane of the cheek, con- 

 tinuous with that forming the gums, is red in colour and about 2 mm. 

 in thickness. A row of small papillae will be noticed following the line 

 of the upper teeth. Upon each papilla opens a duct of the dorsal 

 buccal glands. A similar row of papillfe Avith the openings of the ducts 

 of the ventral buccal glands may be discovered opposite the mandibular 

 cheek-teeth towards the angle of the mouth. 



The most conspicuous object on the inner surface of the cheek is an 

 elevation of some size, i\\q papilla salivalis, opposite the anterior part 

 of the third maxillary cheek-tooth. On the summit of the papilla is 

 the opening of the parotid duct. 



