1896.] MAMMALIAN DENTITION. 563 
region, thus resembling the condition which I described in the 
Macropodide (28. p. 467). 
The antero-external cusp (protocone of Scott) of dpm. 4 develops 
first, the antero-internal or deuterocone second, and the tetaro- 
cone third, the tritocone being wanting. 
The Molars. 
m. 1. m.2 
Of the three molars of the adult, aaa 
in my specimens. The enamel-organs of these two teeth, both 
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 in 
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 in the jaw the structure essential for 
the production of a second set of molars. 
In addition to this lingual growth, we 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 7-2, 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 replacing sets. 
Further consideration of these sets will be found in my general 
conclusions. 
are alone developed 
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 quinquetubercular, being 
modified trituberculo-sectorial teeth, in which the heel has 
1 In the descriptive portion of this paper Osborn’s nomenclature of the 
molar cusps (1) is used, but I do not thereby imply that I believe in all cases 
the homology of the cones has been correctly interpreted ; in fact, in the general 
summary I endeavour to show that the cusp usually termed the protocone in 
the Insectivorous molars is not homologous in all the genera, 
