TOOTH-GENESIS IN THE CANIDiE. 449 



which is an indication of a cusp. Oii the inner side is a distiDcfc 

 cingulum, giving rise to well-marked anterior and posterior cusps 

 (ca and cp), the former lying slightly to the inner side of the 

 main cone, as is the case in the corresponding tooth of the upper 

 jaw. 



The second functional deciduous premolar (dpm.^) has exactly 

 the same characters, but more pronounced, especially in the case 

 of the cusp {g) on the posterior slope of the main cone, which is 

 here of cousiderable size. 



The third functional deciduous premolar, or lower carnassial 

 (dpm?), is a large and massive tooth and of considerable antero- 

 posterior extent. It has a prominent cone about the middle of 

 the external face, the Protoconid (fig. l,^r'), in front of which 

 is the Paraconid (ca), the free end of which forms a cutting-edge. 

 Posteriorly is a cusp (g^ entering into the formation of the 

 so-called heel, and separated from the Protoconid by a large 

 depression. The cingulum is marked on the posterior half of 

 the internal face of this tooth ; it gives rise to a minute cusp at 

 the postero-external border of the tooth. On the ridge of the 

 cingulum are two well-marked cusps — an anterior Metaconid, 

 the larger, lying at the postero-internal angle of the Protoconid; 

 and posteriorly a smaller cusp. 



It will be noticed that I have refrained from applying names 

 to any but the three primary cusps. I have done so, as I am 

 unable to reconcile the cusps of some of the teeth, notably the 

 lower carnassial, with the descriptions usually given. Even the 

 Paraconid (the cusp usually described as the aiitero-internal), if 

 examined in the lower carnassial, is antero-external, r^ither than 

 antero-internal. 



But, omitting these minor difficulties, is it possible to homo- 

 logize the all-important Protocone ? 



I have been unable to find that any attempt has been made 

 by the upholders of the Tritubercular theory to homologize the 

 cusps of the premolar teeth with those of the molars. Scott (23) 

 believes that in the upper premolars the protocone forms the 

 antero-external cusp, a conclusion with which, as will be seeu 

 below, I entirely agree, and which appears to have been tacitly 

 accepted by Osborn (16 & 17). But these writers do not 

 appear to adopt the view that the main cone of the premolars is 

 homologous with the paracone of the true molars. On p. 443 of 

 his paper cited, Scott states that, " assuming the correctness of 



