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Show 568 MR. M. E. WOODWARD ON [May 5 In the lower molar the protoconid evidently develops first, but it is closely followed by the metaconid, the entoconid, and the hypoconid, the reduced paraconid being last, the order being identical with that seen in Erinaceus. The relation of the milk and permanent dentitions may be thus expressed :- fl 2 3 ( 1 f ? 2 3 4 fl 2 3 T J 1 2 W. C ) 1. V J 1 ! 3 3 • M J L< 1 2 3' U - < 1' ^ 1 (*) 3 4' M ^ ' LI 2 3 [1 {? 2 3 4 1,1 2 3 SOREX. The Shrews are generally regarded as possessing one dentition only, but both Owen (18)andTrauber (25) stated definitely that there was a minute calcified milk-dentition present, Owen ascribing to 4 Crocidura -. milk-teeth, while Trauber states that in 8. vulgaris 7 fi there are = and in Crossopus fodiens ^ deciduous teeth. Leche (9) believes that these authors mistook the calcifying cusps of the replacing teeth for a set of minute milk-teeth-he himself coming to the conclusion, from the material at his disposal, that only one dentition is present in Sorex and Crossopus; this he regards as the successional set, the milk-dentition having been suppressed. M y own observations are based on the examination of one stage only, but it appears to be in a very interesting condition and shows distinctly traces of two dentitions. The specimen measured 32 m m . long, the head length being 8 mm., while from the crown of the head to the posterior flexure of the body it was 13 mm., being just 1 m m . shorter than Leche's youngest stage. The Incisors. ^~.-These in the adult are two enormous procumbent teeth, and in m y foetal specimen are much in advance of the other teeth. The enamel-organs of these two teeth exhibit strong lingual growths of the dental lamina (Plate X X V . fig. 15, dl.), so large and swollen, indeed, as to suggest the development of a successor; but such a condition could not possibly have been overlooked for it would involve the replacement of a large tooth at a comparatively late period, whereas the only suggested milk-teeth (Owen and Trauber) are said to be minute. The 2nd upper incisor is backward in its development, but its enamel-organ exhibits a marked labial growth (fig. 16, d_K2); this latter being swollen at its free end and slightly indented, evidently represented the enamel-organ of a predecessor to i^2 in a vestigial condition. A similar but non-indented labial growth is found related to ij? (fig. 17), this condition being repeated in connection |
