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Mr. E. B. Poulton. True Teeth in 



[Feb. 9> 



part of the molar series in the higher mammals. Examining the 

 sections from the front backwards, the first tooth appeared a little 

 behind the anterior margin of the epithelial elevation, which appears 

 to represent the developing horny plate which in the adult is the 

 functional representative of true teeth. The teeth seem to form a 

 tolerably straight line, extending internally to the horny plates, and 

 passing considerably further backwards than the latter.* Owing to 

 imperfections in this part of some of the sections, I could not deter- 

 mine the exact number of teeth with accuracy, but they appear to be 

 five or six in number on each side.f The most anterior of these is 

 of a different character from the others, and is apparently separated 

 from them by an interval which is longer than in other cases. 

 This anterior tooth is the most developed, and its apex extends so 

 far towards the surface that it nearly touches the epithelium. It is a 

 pointed cylindrical tooth, directed vertically downwards. The fourf or 

 five posterior teeth are of uniform shape. Their structure, appearance, 

 and relation to the surface are shown in fig. 1 ( X 40) . The two 

 chief cusps of each of these broad teeth arise from the inner side of 

 the surface.^ 



The structure of the enamel- cap is entirely normal, except that 

 capillaries are certainly present in the middle membrane, intruding 

 from without. The inner layer of long enamel cells is very distinct 

 (see figure). No enamel is formed from them at this stage, except 

 probably in the case of the anterior tooth. § The dentine is quite normal 

 in appearance and formation in the posterior teeth, except that the 

 striation due to dentinal tubules can only be made out beneath the 

 apex, but this may be due to the condition of the specimen or to method 

 of preparation.!] The inner part of the dentine stains faintly in 

 carmine, and shows the striation ; the outer part does not stain, and 

 appears homogeneous. The dentine of the anterior teeth is much 

 thicker, and is not of normal character || in its inner part, its outer 

 part resembling that of the other teeth. 



* In the lower jaw the teeth appear to lie exactly beneath the developing plate. 

 This may be the case in the upper jaw also, for the epithelium was in a damaged 

 condition, and I may have been mistaken in my first identification of the unde- 

 veloped horny plate. Comparison with a skull of the same age strongly supports 

 this conclusion. — Feb. 6, 1888. 



f I have since found that the teeth are fewer in number, probably three 

 being present upon each side of each jaw. The two posterior teeth have many 

 cusps, and the two largest of these looked like separate teeth in sections. The true 

 shape has been shown by a dissected preparation of the lower jaw. — Feb. 6, 1888. 



% In the lower jaw the two chief cusps arise from the outer side of the teeth.— 

 Feb. 6, 1888. 



§ Eecently prepared sections, made in order to decide this point, have shown 

 that enamel is certainly present. — Feb. 6, 1888. 



|| Eecently prepared sections have shown that the dentine is of the usual struc- 



