I I 
L 
1896. ] MAMMALIAN DENTITION. 565 
seem rather strange, but we must bear in mind the fact that this 
cusp is apparently of little importance in Hrinaceus, as it is very 
small in adult and may be almost wanting on m. 2. 
A further consideration of these cusps will be found at the end 
of this paper. 
The relations of the milk and permanent teeth of Erinaceus may 
be represented as under, the reduced teeth being indicated in 
italics, those which never cut the gum and are entirely functionless 
being enclosed in brackets, while the functional ones are repre- 
sented by ordinary figures (Winge, 26) :— 
So far as I am aware, no young specimens of this genus have been 
examined in the fiesh for their tooth change. Thomas (23) has, 
however, published a bare statement of two dentitions in this genus, 
based, I believe, on a young, dried skull in the British Museum 
collection ; but there is a good deal of uncertainty attached to this 
method, for although the jaw has been cut to expose the underlying 
tooth-germs, no actual germs are visible, and one can only surmise 
their existence from the presence of cavities at the roots of the 
functional teeth (Plate XXIV. fig. 12), and by a comparison of 
these teeth with those of an adult specimen. 
The dentition, according to Thomas, is :— 
RR aA oR A LA Sel ok WU Ss cee IP aa 
| | | 
Ik D3) 1 2 3 4 
(ROA Sale Vea aa alg ae 2 ll 23 
di. 3 and dpm. 2 being vestigial. 
The specimen examined by me was a fcetus, with a head length 
of about 49 mm. and a total length of 205 mm. 
The Incisors. 
I.1&i.2 are large and well calcified, each showing a marked 
lingual development of the dental lamina, indicative of a suc- 
cessional tooth. On the other hand, i-3 is more specialized, and 
only present in the permanent set of teeth. In my fcetus this 
tooth was very backward in its development, its enamel-organ being 
but slightly differentiated (pi.3), and exhibited on its labial side a 
large irregular calcification (fig. 10, di.3), provided with a reduced 
enamel-organ ; this is evidently the milk predecessor of i.3, and 
(es) 
Li 2ijud fel rel Renee 4 (1 2 
1 2 @), 3 1. lo @ 3 4 (1) 2 (8) 4. | 
203 ut Vo A 4 bp "2 
GYMNURA. 
