HEAD AND NECK OF THE HORSE 57 



It is worthy of note that in the average mammal there are two 

 sublingual glands on each side of the head. One of these is provided 

 with a single large duct, and is therefore named the glandula sub- 

 lingualis raonostomatica ; while the other, the gl. sublingualis 

 polystomatica,'^ has numerous small ducts opening independently into 

 the floor of the mouth. In the Equidce the gland with the single large 

 duct is absent, and in this respect the members of the horse tribe differ 

 from all the other domesticated mammals. 



The horse's sublingual gland is flattened laterally and extends from 

 the symphysis of the mandible to the level of the third or fourth 

 mandibular cheek-tooth. Its lateral surface is covered by the mylo- 

 hyoid and mylo-glossal muscles, and along a narrow strip close to the 

 upper border, by the mucous membrane of the mouth. The medial 

 surface lies upon the genio-glossal and stylo-glossal muscles and is 

 traversed longitudinally by the duct of the submaxillary gland. The 

 lower border is in contact with the genio-hyoid muscle ; while the 

 upper border causes a linear elevation of the mucous membrane of the 

 floor of the mouth, upon which may be observed the openings of twenty 

 to thirty small ducts (ductus sublinguales minores) on the summits of 

 small papilke. 



The Submaxillar 1/ Gland (Glandula submaxillaris). — The sub- 

 maxillary salivary gland is elongated, laterally flattened, and gently 

 curved with a concavity looking upwards and forwards. It extends from 

 the fossa atlantis to the body of the hyoid bone. Its lateral face is 

 related to the internal pterygoid, digastric and jugulo-mandibular 

 muscles, the tendon of insertion of the sterno-cephalic and the fibrous 

 sheet connecting this tendon with that of the brachio-cephalic muscle. 

 The flattened tendon of the sterno-cephalic muscle, and the fibrous 

 sheet connected therewith, separate the posterior part of the sub- 

 maxillary from the overlying parotid gland. 



The medial surface of the gland is in contact with the diverticulum 

 of the auditory tube, the flexor muscles of the head, the termination of 

 the common carotid artery, the pharynx and larynx, and the tenth and 

 eleventh cerebral and sympathetic nerves. 



The thin concave upper border of the gland is intruded between the 

 jugulo-mandibular muscle and the diverticulum of the auditory tube, 

 and along it the commencement of the duct of the gland will be found. 

 The thicker convex border rests about its middle on the thyroid gland. 



1 M.ovos (monos) [Gr.], single. -rroXvs (polys) [Gr.], many. <^r6/xa (stoma) [Gr.], 

 a mouth. Writers frequently use the terms grandicanalaris and parvicanalaris 

 instead of monostomatica and polystomatica ; but it seems preferable to employ terms 

 that signify the number of the openings rather than the size of the ducts. 



