584 MR, M. F. WOODWARD ON [May 5, 
I have adduced reasons elsewhere (29) to support the view that 
this pre-milk set, ¢. e. the first in order of time, has been completely 
lost in the molar region, and that these labial outgrowths of the 
dental lamina represent the now much reduced milk-dentition—the 
adult molars belonging to the 3rd or replacing set of teeth, the 
lingual continuation of dental Jamina representing a potential 4th 
dentition, the post-permanent series. 
The Molar Cusps. 
On comparing the details of the molar cusp development in the 
various Insectivores which I have examined, one is immediately 
struck with fact that the lower molar cusps in the different forms 
are more constant in the order of their appearance, the protoconid 
developing first in every case, than those of the upper molars: 
these latter fall apparently into two groups—in one the paracone is 
the first to appear, while in the second it is the protocone which 
develops first. A closer inspection shows that a similar subdivision 
of the lower molars can be made; thus in those forms where the 
paracone appears first in the upper molars, we find the supposed 
homologue of this in the lower teeth (the paraconid) ? is the last to 
develop, while those exhibiting the protocone as the first developed 
cusp above show the paraconid as second or third in order of 
development below. 
These facts may be roughly tabulated thus :— 
Group I. (4 genera). Group II. (2 genera). 
1. Paracone. 1. Protocone. 
2. Metacone. 2. Paracone. | 9 eae 
3. Protocone. ot eee ogee 
4. Hypocone. 
(5. Metaconule.) 
1. Protoconid. 1. Protoconid. 
2. Metaconid. 2 or3. Paraconid. | 9 Lonel 
3 (aes 3 or 2. ecnd { gees 
. Heel. 1 7, 
Ypo. 
4, Paraconid. 4. Hypoconid. 
A further examination of these groups reveals the fact that they 
are separated from one another by a second feature, which is 
possibly of greater importance than that of cusp ontogeny ; I refer 
to the fact that the members of group I. possess either quadri- or 
quinque-tubercular upper molars, while in group II. these teeth 
are trituberculate. 
It will be seen, then, that in the only living mammals believed 
to possess unmodified trituberculate teeth (molars and posterior 
premolars) which have been examined developmentally, the order 
of cusp ontogeny is in entire accord with the supposed order of 
1 The condition of this cone in Sorex is uncertain. 
= 
