156 MAMMALIAN DENTITION 



ties appearing in other Anthropoidea and in the Lemurs. The 

 example of Potamogale already illustrated (Fig. 33) shows 

 retention of a deciduous tooth. In other Insectivora indeed the 

 apparent mingling of the milk and permanent dentitions has 

 presented many perplexing problems. In every large collec- 

 tion of canine skulls many are to be found in which the last 

 lower molar has never erupted. In this study it will only be 

 possible to consider briefly some variations in the dentition of 

 Man. 



Generally speaking anomalies of the human dentition, be- 

 yond retention of certain of the milk teeth, are those of varia- 

 tion in position, number and conformation of the permanent set. 



With variations in position of normal teeth in either denti- 

 tion we have nothing to do since these are always of patho- 

 logical origin so far as is known but it is necessary to review 

 rapidly examples of the other types. 



Fig. 55 shows a variation met with perhaps more frequently 

 in the skulls of American aborigines than in those of the 

 White race. An extra tooth occurs between the upper median 

 incisors which seem normally formed in every respect. From 

 the appearance of these teeth it is obvious that the anomalous 

 incisor cannot have occurred as the result of division of a 

 normal incisor, a process known as schizogenesis. With it must 

 be contrasted the split incisor which is occasionally observed. 

 Inasmuch as genuine subdivision may result in the production 

 of an extra tooth between the central and lateral incisors or 

 between the lateral incisor and the canine, it has been stated 

 that our normal upper incisors represent numbers 2 and 4 of a 

 series consisting originally of five teeth such as occurs today 

 in the Opossum. This interpretation however cannot be 

 considered seriously in view of the very different modes of 

 origin of the two types of supernumerary incisors just men- 

 tioned. Again it has been suggested that subdivision or diminu- 

 tive size of the lateral incisor has been brought about by the 

 occurrence at and the splitting by the junction of the premaxil- 

 lary and maxillary elements of the upper jaw of the rudiment 



