152 THE MAMMALIA. 



being allowed free play upon an almost level, or 

 even a somewhat raised surface. 



All Ruminants possess the above-mentioned 

 typical molars with the enamel crescents running 

 in the direction of the longitudinal axis of the 

 skull, which, of course, present a very different ap- 

 pearancewithin the boundaries of the generic 

 characteristics according to age and wear. Fig. 

 21 shows an, as yet, uncut fourth right molar of 

 a calf as seen from the front and the inner side. 

 It seems to consist of two almost quadrilateral 

 prisms, both terminating on the outer and inner 

 side, in two curved flaps (A-I and a-i). All the 

 surfaces, which pass over into various curves and 

 folds, one within the other, and are lost in the interior 

 of the tooth, consist of the, as yet, imperfect and 

 still somewhat soft layer of enamel. Below it is 

 the dentine, which is likewise just beginning to 

 develop, and round about in the depressions, between 

 A and i and a-i, we find the incomings of the 

 cement which is still a membraneous formation. 

 Now, if we take this embryo tooth and compare 

 it with the polished edge of one of the already cut 

 front teeth (Fig. 21, n), we shall at once obtain a 

 clear idea of the relation of the enamel folds and 

 edges of the molar of a full-grown animal. The 



