294 



SPLANCHNOLOGY, 



incisor, but the contour of the various parts is much more 

 irregular. There are generall}' two infundibula containing a 

 large quantity of cementum, a layer of which also covers the 

 greater part of the external enamel. 



The crown of the upper molars is somewhat cubic ; their 



external surface presents 



two grooves running from table to 

 root, the anterior being the deeper. 

 The crown of the lower molars is 

 narrower, but longer than that of the 

 upper ones, and has only one groove. 

 The inner surface of the upper molars 

 is not so deep as the outer, while the 

 inner surface of the lower ones is the 

 deeper ; the two lower rows diverge 

 towards the back of the mouth, while 

 the two upper rows are rather convex 

 externally. The molar grinding sur- 

 A A, External crustapetrosa; B, Exter- face is Very irrcgular, owing to the 



nal enamel ; C, The Dentine ; -D D, • i i i i c • j. j. 



Internal enamel surrounding the infun- Variable hardnCSS of itS COmpOnCUtS. 



dibuia: E E, crusta petrosa occupying j^ horsc may havo Supplementary 



the infundibula. 7/. ii 



molars, or wolf teeth; these are 

 small, and placed one on each side of the jaw, anterior to the 

 first molars ; they are usually shed with the milk teeth. 



The teeth which replace the deciduous or milk molars are 

 situated anteriorly, and are distinguished as lyreifnolavs. 



Fig. 97. 

 Transverse section of a molar tooth. 



DENTAL FORMULA. 



A dental formula expresses in a concise manner the number 



and position of the teeth possessed by an animal. The numbers 



are written somewhat in the form of fractions, and prefixed are 



the initial letters of the names of the various teeth. Thus, i. 



stands for incisors, c. for canines, 79. m. for premolars, and m. for 



molars. For example, the molar teeth of the dog are thus 



2 — 2 

 represented : — m. ^ — ^ ; this means that there are two molars on 



each side in the upper jaw, and three on each side in the lower 



jaw. In the ox the incisors are i. :: — ^j, or none whatever in the 



upper, and three on each side in the lower jaw. The full dental 

 formulae of the horse are as follows : — 



