THE MOUTH. 355 



The follicle which develops these three elements of the molar tooth, 

 offers at the bottom an enormous papilla divided into several lobes, which 

 lie together for their whole length ; lodged in the internal dental cavity, it 

 gradually decreas3S, like the papilla in the other kinds of teeth, as the 

 cavity becomes diminished by the formation of new dentine. Opposite to 

 it are two long papillse, which occupy the enamelled infundibuli. 



" It was believed for a long time that the molars of Solipeds were all 

 persistent teeth. This error, founded on the authority of Aristotle, was so 

 deeply rooted, that although Kuini, towards the end of the sixteenth century, 

 had discovered the existence of two temporary molars, Bourgelat did not 

 believe it when he founded the French Veterinary Schools-and was only con- 

 vinced when Tenon had proved by specimens, in 1770, that the first three 

 of each arcade are deciduous. 



" The replacement of these twelve molars is not at all like what happens 

 with the incisors. The molar of the adult grows immediately beneath the tem- 

 porary one, and divides its two fangs into four, until its body is reduced to a 

 simple plate and falls off, allowing the contracted summit of the permanent to 

 appear ; and this grows up until it is soon on a level with the others in the row. 



" The first replacing molar is always a little more elongated than that 

 which it succeeds, and it most frequently expels at the same time the sup- 

 plementary molar ; so that if forty-four teeth be developed in the male 

 Horse, it is very rare that they are all present at the same time." 



7. The Mouth in General. 



We will now consider, as a whole, the cavity whose various parts have 

 been studied in detail, and examine, successively, its general disposition, 

 capacity, and mucous membrane. 



General disposition and capacity of the mouth. The mouth being elon- 

 gated in the direction of the head, offers a great antero-posterior diameter, 

 and two small diameters one vertical, the other transverse. The first 

 extends from the base of the epiglottis to the anterior opening of the mouth ; 

 the second, from the palate to the floor of the mouth ; and the third, from 

 one jaw to the other. When the jaws are in contact, the space included 

 between these limits is divided into t\vo regions: one central, the other 

 peripheral. The first is circumscribed by the dental arches ; the second 

 is comprised between these arches on the one side, and the cheeks and 

 inner aspect of the lips on the other. It may, therefore, be remarked, 

 that the capacity of the mouth is almost null in these regions. The cheeks 

 and lips, in reality, lie almost exactly against the alveolar arches, and the 

 tongue, in contact with the palate by its superior surface, almost entirely 

 fills the central region. If the jaws separate from one another, and the 

 cheeks recede from the dental arcades, the cavity of the mouth becomes 

 enlarged in proportion as these movements are extensive. It must be 

 remembered that the separation of the jaws is effected in an angular manner, 

 and that the dilatation produced in the mouth by this movement is greater 

 before than behind, the opening of the angle comprised between the two 

 jaws being directed towards the entrance of the cavity. 



Mucous membrane. The walls of the buccal cavity are covered by a 

 tegumentary membrane, which we have hitherto only examined in parts in 

 the different regions it covers, but which, it is to be noted, forms here a 

 single and continuous layer, the mucous membrane of the mouth. 



This membrane is continuous with the external skin at the margin of the 



