THE MOUTH. 411 



marked in the Ass than the Horse. It is worthy of notice, that the glands 

 composing this layer throw all their secretion into the mouth — that is, on the 

 anterior face of the soft palate. 



4. Mucous membranes. — The soft palate is covered on both its surfaces by two 

 mucous layei-s, one anterior, the other posterior, united, as has been remarked, at 

 the free border of the organ. The anterior is continuous, above, with the mucous 

 membrane of the hard palate ; on its sides, with that which covere the base of 

 the tongue. In structure it is the same as the buccal membrane ; its epithelium 

 is stratified and tesselated. The other layer is nothing more than the pituitaiy 

 membrane extended over the posterior surface of the sei)tum, and thence to 

 the lateral surfaces of the pharynx. It will be more fully described with the 

 latter. 



5. Vessels and nerves. — The soft palate is supplied with blood by the 

 sfaphyUne and pharijngeal arteries. The nervous filaments tliis partition receives, 

 emanate from the fifth pair of cranial nerves (superior maxillary branch), and 

 from Meckel's ganglion ; they form the staphyline or posterior palatine nerve 

 (Fig. 215, 8). 



The superior maxillaiy branch is entirely sensitive, and yet the staphyline 

 nerve goes to tegumentary, glandular, or contractile organs. How can it fulfil 

 this double function ? By receiving filaments from Meckel's ganglion, which has 

 motor fibres derived from the facial nerve. 



Functions. — During the act of deglutition, the soft palate is raised to 

 enlarge the isthmus, and allow solids or liquids to pass through. The description 

 given of this septum, permits us to understand how it plays the part of a valve, 

 in rising freely while the alimentaiy bolus or mouthful of fluid passes from the 

 mouth into the oesophagus, across the pharyngeal vestibule, but never allowing the 

 matters which have once entered the oesophageal canal to return into the buccal 

 cavity. Also why, when any obstacle is opposed to the descent of aliment into 

 the oesophagus, after it has cleared the isthmus of the fauces, or even when the 

 animal vomits, the matters arrested in their passage or expelled from the stomach 

 are ejected by the nasal cavities, after flowing over the posterior surface of the 

 soft palate. This disposition of the pendulous curtain, in forming a complete 

 partition which hermetically seals the orifice of communication between the 

 mouth and pharynx, likewise sufficiently explains why, in noraial circumstances, 

 Solipeds respire exclusively by the nostrils. 



6. The Teeth. 



Passive agents in mastication, the teeth are hard organs, bony in appearance, 

 implanted in the jaws, and projecting into the interior of the mouth, in order to 

 bruise or tear the solid alimentary substances. 



Identical in all our domesticated animals, in their general aiTangement, their 

 mode of development, and their structure, in their external conformation these 

 organs present notable differences, the study of which offers the greatest interest 

 to the naturalist. For it is on the form of its teeth that an animal depends for 

 its mode of alimentation ; it is the regime, in its turn, which dominates the 

 instincts, and governs the diverse modifications in the apparatus of the economy ; 

 and there results from this law of harmony a striking correlation between the 

 aiTangement of the teeth and the conformation of the other organs. 



Compelled by the limits of our task to confine oureelves to the purely 

 descriptive part of the dental apparatus, we cannot stop to notice the interesting 



