268 ELEMENTARY ANATOMY, [LESS. 



outer ends of these two transverse ridges. We find such a 

 structure in the Tapir. 



In the Rhinoceros, Horse, and the Ruminants, the essential 

 structure of the Tapir's tooth persists, but is modified by 

 greater and greater obliquity of the transverse ridges and by 

 the development of supplementary processes running more 

 or less at right angles to the transverse ridges. 



FIG. 243. GRINDING SURFACE OK SECOND UPPER MOLAR OF A CAMEL, 

 showing the double crescentic folds which have their convexities turned inwards. 



In the Ruminants the transverse ridges are so much in- 

 clined backwards and inwards, that they come to be almost 

 parallel with the external wall, thus forming the well-known 

 double crescents with a deep excavation between them seen 

 in the molars o f Sheep. 



In the Horse this excavation is filled up with " cement," 

 and the pattern is complicated by the development of acces- 

 sory processes from the convex, or inner side of the trans- 

 verse ridges. 



MRY.OCHLORW 



FIG. 244. GRINDING SURFACE FIG. 245. GRINDING SURFACE 

 OF RIGHT LOWER MOLAR. OF RIGHT LOWER MOLAR. 



Tn the lower jaw an analogous series of modifications has 

 similar results. In the insectivorous type these modifications 

 result in a pair of triangular prisms (produced by the con- 

 nection by ridges of the five cusps answering to the five cusps 

 developed in the lower molar of man) ending in sharp points, 

 as in the Mole ; or in a single prism, as in the Golden Mole, 

 Chrysochloris. The prisms are reversed in position as com- 



