TEKTII.] 



MODERN VETERINAKY PltACTlCE. 



[teeth. 



aud clmrnctoristio of such. In another part 

 of his work, Profi-ssor Owen Ht-locts tho 

 liorso ns an cxatuplo of bucU herbivorous 

 dentition. 



Tlio f^rinding teetli of this uiiiiiuil are "six 

 in number, on eaeli side of both upper and 

 lower jaws, with tliick, square crowns of ^reat 

 loiigtl), and deeply implanted in tho sockets; 

 those of the upper jaw being slightly curved. 

 AVhen the summit, or exposed ends, of these 

 teeth begin to be worn down by inaatication, 

 the interblended enamel, dentine, and cement, 

 show the pattern figured in tho accompanying 

 engravings. It is penetrated within by a 

 valley, entering obliquely from behind for- 

 wards, and dividing into, or crossed by, the 

 two crescentic valleys, which soon become 

 insulated. There is a large lobe at tho 

 end of the valley. The outer surface of the 

 crown is impressed by two deep longitudinal 

 channels. In the lower jaw the teeth are nar- 

 rower, transversely, than in the upper jaw, and 

 are divided externally into two convex lobes, 

 by a median longitudinal fissure ; internally 

 they present three principal, unequal convex 

 ridges, and an anterior and posterior narrower 

 ridf^e. All the valleys, fissures, and folds, in 

 both upper and lower grinders, are lined with 

 enamel, which also coats the whole exterior 

 surface of the crown. Of the series of six 

 teeth in each jaw, the first three, p 2, 3, 4, 

 are premolars ; the rest, m 1, 2, 3, are true 

 patternof the folds of enamel I molars, used lor the purpose of grinding the 



that penetrate the substance of the tooth, and j food." 



add to its triturating power, 



is almost endless ; but it 



would seem that the folds 



have an invariable tendency 



to a transverse direction 



across the crown of the ^^ 



tooth in the rodents. Tliis ;3=.-' 



direction relates to the shape ^^- — =- — ■ - 



of the joint of the lower y, , , / ; 



jaw, which almost restricls 



it to horizontal movemcn: - 



to and fro, during the act ^ 



of mastication. In the trne- 



,..,,,. . , GRINDIVG SURFACES OF THE UPPKR AND LOWER MOLARS OF A HORSi.. 



hooted herbivorous annuals, 



in which the joint of the lower jaw allows The accompanying plates show the appear- 



a free rotatory movement, the folds of ance of the teeth at diilerent ages, and indi- 



enamel take other forms and directions, cate the age of an animal by their lonu 



with modifications, constant in each genus, and marks. 



' 171 



ns in bone, but consists commonly of two or 

 more tissues, characterised by the proportions 

 of their earthy and animal constituents, and by 

 the size, form, and direetion of the cavities in 

 tho animal basis, which contain the larth, the 

 fiuid, or the vasenlar pulji. 



" The tissue which fiu-ms the body of the 

 tooth is called ' dentive.' 



" The tissue which forms the outer crust of 

 the tooth is called the ' cement.' 



" The third tissue, when present, is situated 

 between the dentive and cement, and is called 

 ' enamel.' " 



The teeth called compound, or comjdex, in 

 mammalia, differ, as regards their composition, 

 n. only by the difi'ereut propor- 



tion and disposition of con- 

 stituent tissues. The accom- 

 panying cut isthelongitudinal 

 section of the incisor of a 

 iiorse ; d is the dentive, e 

 the enamel, and c the cement, 

 a laver of which is reflected 

 into the deep central depres- 

 sion of the crown ; s indicates 

 the coloured mass of tartar 

 and particles of food which 

 fill up the cavity, forming the 

 " m.ark" of the horse-dealer. 

 In pursuing this interest- 

 ing subject still further, we 

 find that the variety in the 



/7 



^^- 



SECTION OF HORSE S 

 INCISOR. 



