256 Mammalia, 



tMs process that the tendon of tlie tensor palati muscle passes ; 

 a muscle that fixes and renders tense the lateral parts of the 

 soft palate. 



Tracing the edge of this bone backwards, a small lip will 

 be found, in the mucous membrane, covering the termination 

 of a tube. This tube, which is closely united to the pterygoid 

 plate, covered by the mucous membrane, and opens into 

 the Pharynx, is the Eustachian tube, a canal by which the 

 cavity of the tympanum is rendered continuous with the 

 cavity of the Pharynx ; in other words, a canal by which the 

 tympanic cavity of the ear communicates with the external 

 air. The upper part of this canal was noted in a previous 

 stage of this dissection (p. 237). 



The Pharynx is that cavity that extends obliquely down- 

 wards and backwards above the velum palati (which separates 

 it from the mouth), and forms the backward prolongation of 

 the posterior nares. We have just noted the slit-like open- 

 ings of the Eustachian tubes on each side ; below these we 

 oome to the Isthmus of the Fauces^ a narrowed channel between 

 the Pharynx and the mouth, or rather between the free bor- 

 der of the velum palati and the Epiglottis, whose size is 

 altered by the elevated or pendent position of the soft palate. 



The posterior border of the soft palate in man presents in 

 the centre a conical pendulous body called the Uvula, but 

 this is absent in nearly all other animals. In the Horse, the 

 velum palati is so much developed that the isthmus is kept 

 constantly shut, except during the passage of food or water, 

 and the animal is unable to breathe through his mouth;* but 

 in the Sheep it is not so complete and pendulous, conse- 

 quently the isthmus is generally open, thus allowing the 

 animal both to breathe through the mouth and to regurgitate 

 its food in the act of rumination. 



* Strangeways. 



