ANOMALIES OF THE HUMAN DENTITION 161 



quent in the Gibbon and in the Old-World Monkeys in which 

 latter family their rarity may be connected with the tendency 

 to elongation of the normal third molar. Among American 

 Monkeys Atelens, also an advanced form, shows this anomaly 

 most often and again the very specialized genus Lemur exhibits 

 it more frequently than the relatively primitive genera of the 

 Lemuroidea. In other orders the anomaly appears constantly 

 in the aberrant canine Otocyon, in the very specialized Armadil- 

 los and toothed Whales, and among Marsupials in the Banded 

 Anteater. It seems, therefore, to be a secondary progression 

 occurring more frequently with increasing specialization until 

 it becomes normal in very aberrant types.* 



We have already commented upon the relative instability 

 of the second and third molars in the human dentition. The 

 second upper especially in White races tends to lose its hypo- 

 cone (see Fig. 54). It may lose its metacone also in which 

 case the not infrequent condition represented in Fig. 56-D 

 results. Again both these cusps may be rudimentary or absent 

 in the third upper molar which may be reduced indeed to a 

 simple stump-like tooth (Fig. 56-2?). Of the lower molars the 

 second loses its hypoconulid more frequently than the third 

 (see Fig. 53) and only the first exhibits this cusp with any 

 regularity. 



Regarding the increase in number of cusps of the molars there 

 are several types and the causes underlying these differ in them- 

 selves. One not infrequently finds an accessory cusp on the 

 second or third molar fused with the paracone in the upper 

 (Fig. 56-F) or with the protoconid in the lower tooth (Fig. 56-(x ) . 

 To these Ave shall return in a moment. There is sometimes a 

 supernumerary cusp on the mesial side of the molar fused with 

 the anterior aspect of the protocone in the upper tooth (Cara- 

 belli's tubercle, Fig. 56-lf), or with the entoconid of the lower. 

 The former of these is stated by some to represent the cingular 

 cusp in the corresponding situation in the upper molar of the 



*It is probable that the six successive molars of the Elephant really represent three 

 deciduous and three permanent teeth. 



