THE MOUTH. 



421 



"With regard to the table of the tooth, it inchnes, as we have already 

 mentioned, outwards in the lower jaw, and inwards in the upper— a circumstance 

 which prevents the lateral movements of the jaws taking place without separa- 

 tion of the incisors, which separation removes them from friction." In the virgin 

 molar, this face is completely covered with enamel, and irregularly undulated. 

 In it may be recognized the two infundibular openings, which are prolonged in 

 the interior of the organ to the extremity of the root, and are almost entirely 

 tilled with cement at the period when the tooth has completed its evolution ; 

 they are only void before the secretion of this crusta petrosa. In the tooth 

 which has been worn, this frictional surface assumes a particular aspect, which 

 will be indicated with most advantage to the student by examining the structure 

 of the molar. 



" The root, if examined a short time after the eruption of the free portion, 

 looks only like the shaft of the latter, without any appearance of fangs, and 



Fig. 233. 



PROFILE OF THE UPPER TEETH OF THE HORSE, MORE ESPECIALLY INTENDED TO SHOW THE 

 molars; the fangs have been EXPOSED. 



a, Molai" teeth ; b, supplementary molar ; c, tusk ; d, incisors. 



has internally a wide cavity. It is not until the tooth begins to be pushed from 

 the alveolus and its crown to become worn, that its fangs are formed ; these are 

 at first hollow, and afterwards filled, as well as the cavity of the tooth, by the 

 formation of a new quantity of dentine. From this time the fangs cease to 

 grow ; but the tooth, constantly projected beyond the alveolar cavity, allows the 

 walls which enclose it to contract ; so that, in extreme old age, it happens that 

 the shaft, completely worn away — instead of the tooth — leaves several stumps 

 formed by the fangs. 



"The molars of the two jaws exhibit a variety of roots. In the molars 

 terminating the arches, either above or below, or at the extremities of these, 

 there are three ; while the intermediate molars have four fangs in the upper jaw, 

 and only two in the lower. 



"The molars are separated from each other by their embedded portion, 

 particularly at the two extremities of the arch ; an arrangement which 

 strengthens them by throwing the strain put upon the terminal teeth towards 

 the middle of the line." 



The structure of the molars resembles that of the incisors, though it is much 

 more complicated. The internal cavity is extremely diverticulated, and enveloped 

 by the dentine. The enamel is applied in a layer over it, and is doubled in its 

 external culs-de-sac exactly as in the incisors. There is also on the table of the 



