72 P. N. Bosc—History of the Extinct- Carnivora. 
Pigs and the Moles. But in Kocene times, this number, as first 
noticed by Professor Owen, was the rule, instead of being the 
exception. 
(4.) Upper Jaw.—In Gymnura the first two molars (m. 1 and 
m. 2) are each composed of four tubercles interconnected by ridges, 
the ridge connecting the postero-external with the corresponding 
internal tubercle being oblique and swelling about half-way into a 
small mammillon, as in the Pliolophus of, Prof. Owen. The last 
molar, which is the smallest, has become subtriangular by the 
reduction of the postero-internal tubercle. This process of reduc- 
tion has not been carried so far in the last false molar (pm. 4), the 
homologue of the sectorial tooth of the Carnivora. It is the largest 
premolar ; the anterior of the two external cusps is developed at the 
expense of the posterior one, the former being the most elevated in 
the entire molar series. It inclines slightly backwards, is mapped 
off by a small notch from a rudimentary accessory cusp in front, and 
descends posteriorly into a low horizontally extended portion (the 
representative of the posterior outer tubercle). Of the two inner 
tubercles, the posterior is smaller than the anterior. In premolar 3, 
the former has aborted altogether; this tooth is composed of a large 
pointed, trihedral, external cusp (similar to the corresponding cusp of 
pm. 4), with a rudimentary anterior accessory cusp in front and the 
remains of the posterior tubercle behind ; there is only one internal 
tubercle, so that the tooth is three-fanged. There is nothing remark- 
able in the remaining teeth, except that the canine is two-fanged, 
conical, and curved inwards. If this tooth became one-fanged, 
sharper, longer, and more trenchant, as in Centetes, we would have 
the typical canine of the Carnivora. If, as in the Moles, Hedgehogs, 
etc., the antero-internal tubercle of the third premolar (which has 
the form of a sectorial) aborted altogether, we would get the corre- 
sponding false molar of the Carnivora. ‘The fourth premolar of 
Gymnura is hardly distinguishable from the sectorial of Procyon, one 
of the Suburside. If the inner and hinder tubercle vanished 
entirely, as it does in Talpa, Glisorex, Hriculus, Centetes, etc., the 
tooth would assume the form of the normal sectorial of the 
Carnivora. A similar modification in the first and second molar 
teeth would give us a series of three-fanged teeth, triangular in 
section, with two outer lobes and an inner tubercle. Such a sue- 
cession of ‘“sectorials”” is presented by so many Insectivores, that it 
may be considered to be the normal condition in that order. And it 
is very strange, indeed, that eminent comparative anatomists have 
failed to find a parallel for a similar modification of the molar teeth 
in the Hocene Carnivores, except amongst the Didelphia. The 
hindermost molar is very variable in form and size in the order of 
the Insectivora ; it is small and transverse in Erinaceus. 
All the Eocene Carnivores, with one or two exceptions, have seven 
molars on each side of the upperjaw. The incisors are always three in 
number, as in the typical Carnivora; in the Aplacental flesh-eaters, 
on the other hand, the number of incisors is invariably more than 
three. In Arctocyon, the sectorial, as may be inferred from its 
