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Show 1896.] MAMMALIAN DENTITION. 565 seem rather strange, but we must bear in mind the fact that this cusp is apparently of little importance in Erinaceus, as it is very small in adult and may be almost wanting on m72. 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 represented by ordinary figures (Winge, 26) :- !•< fl 2 3 1 2 (8), (i) 2 (sy L 2 3 fl C^ (j); 11 ** ^ 0 2 3 4 1 2 4 fl 0 (2) 3 4 (1) 2 (3) 4. M j 0 (2) (5') 4'°r(i) (3) 4' iU,sj tO 2 4 1 4 [1 GYMNURA. 2 3 2 3 So far as I am aware, no young specimens of this genus have been examined in the flesh 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 :- fl 2 3 fl fl ' 1 O Q 1 A,ll 2 3' 1 1' \ 2 3 2 3 4 4 fl 2 3 ^ 1 2 3 U 0 3 4 12 3 4 M.<( \\ 2 3 d'-3 and dpm. 2 being vestigial. The specimen examined by me was a foetus, with a head length of about 49 mm. and a total length of 205 mm. The Incisors. 1-1 & 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 foetus this tooth was very backward in its development, its enamel-organ being but slightly differentiated (pi-J^), 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 |
