1896.] MAMMALIAN DBNTITIOIT. 563- 



region, thus resemblino; the condition which I described in the 

 Macropodklce (28. p. 467). ■ 



The antero-external cusp (protocone of Scott) of dpm. 4 develops 

 first, the antero-iiiternal or deuterocone second, and the tetaro- 

 cone third, the tritocone being wanting. 



The Molars. 



Of the three molars of the adult, -^7^ — — . are alone developed 

 lu. 1, m.'i ' 



in my specimens. The enamel-organs of these two teeth, botli 



above and below, exhibit slight lingual continuations of the dental 



lamina; consequently these teeth do not develop in connection, 



with the most deeply-seated portion of the dental lamina, but iu 



relation to that situated nearer to the surface of the gum. The 



presence of this lingually-placed continuation of the dental lamina 



indicates that there is latent iu the jaw the structure essential for 



the production of a second set of molars. 



In addiliou to this lingual growth, wo find also a slight but 

 constant labial outgrowth from that portion of the dental lamina 

 connecting the enamel-organ of the functional molar with the oral 

 epithelium. If this labial growth be compared with the vestiges 

 of the milk-dentition seen in connection with i. 3 and 172, it is 

 found that it is impossible to distinguish these structures from one 

 another, they being precisely similar in their relations to the 

 dental lamina and to the adjacent teeth, differing only in the fact 

 that the labial growth connected with the molars is the most 

 reduced. 



We find, then, in the molar region indications of three sets of 

 teeth — a labial vestigial set, then a functional set, and lingual to 

 this a structure capable of producing one or more rgplaciiig sets. 

 Further consideration of these sets will be found in my general 

 conclusions. 



The Molar Cusps '. 



Erinaceus in the adult condition has three molar teeth in each 

 jaw, the first of these being large, while -^ are reduced. 



The first two upper molars are quinquetubercular, being pro- 

 vided with two well-developed external cones, the paracone and! 

 metacone, two internal ones, the protocone and the hypocone, 

 together with a small central metaconule, this last being the most 

 variable constituent. In addition there is a slight but complete 

 cingulum. 



The lower molars (1 & 2) are also quiuquetubercular, being 

 modified trituberculo-sectorial teeth, in which the heel has 



' In the descriptive portion of this paper Osborn's nomenclaluro of the 

 molar cusps (13) is used, but I do not tliereby imply tliat I believe in all cases 

 tbe homology of the cones has been correctly interpreted ; in fact, in the general 

 summary I endeaTOur to show that the cusp usually termed the protocone in 

 the Insectivorous molars is not homologous in all the genera. 



