TEETH OF THE MESOZOIC MAMMALS 



19 



Dromaiherium has three premolars and seven molars, Imt the number 

 in Microconodon is quite uncertain, as only four of the series are preserved. 

 The molars agree in one particular, which separates them widely from 

 other Mesozoic genera, viz., in the imperfect division of the fangs. This 

 division is indicated merely l>y a depression at the base of the crown, as 

 in the genus Dim<'tro<I<>ii. among the Theromorph * reptiles. 



p 



FIG. 3. No. 1. Microcoiwdoii tenuirogtris. The outer surface of the right mandibular rarnus, 

 enlarged. The two premolars preserved are the first and third, with the fang of the second 

 between. The space behind the third was occupied either by a fourth premolar and the first 

 molar, or by the first and second molars. The molars preserved are, therefore, either the second 

 and fourth, or the third and fifth. The dotted outlines are purely conjectural. 



la. The same, natural size. I/). The fonrth t or fifth molar, much enlarged. 



No. 2. Dromathcrium syli-cstrc. The inner surface of the left mandibular ramus. enlarged. 

 2a. The same, natural size. 26. The second molar, much enlarged. 



ABBREVIATION'S. o. Angle ; c. canine : en. condyle ; cr. coronoid ; i. incisors ; m;i. mylohyoid 

 groove t ; i. molars ; p. premolars. 



Ill all other respects these mandibular raini differ widely. The Micro- 

 conodon ramus is two-thirds the length of that of Di'mn/////, rum/ ; it is 

 flattened and slender, with a nearly straight lower border beneath the 

 molar alveoli, and a characteristic depression of the border which possibly 

 represents the angle of the jaw, as in Prof. Chven's genus PC/V/////.S (Fig. 16.) 

 The coronoid process is low and the vertical diameter of the jaw at this 

 point is very narrow. This ramus offers a great contrast to that of 



*[Dimetrodon is now classified with the Sphenodon-like reptiles. ED.] 

 t[Now believed to be the groove for Meckel's cartilage. ED.] 



