ON THE DEVELOPMENT OF THE TEETH 



very obvious. The epithelium of the follicle forms a thick layer, 

 which sometimes, when the upper wall is stripped back, adheres to it — 

 sometimes remains as a cap investing the papilla. Even when the 

 latter does not take place, shreds of the epithelium frequently adhere 

 to the papilla in the form of irregular, more or less cylindrical 

 nucleated cells ; as often, however, the papilla, whether any of the 

 proper tooth substances be formed or not, has nothing adherent to it, 

 but presents a perfectly smooth sharp edge. Other portions of the 

 epithelium, particularly towards the bottom of the follicles, are more 

 or less altered and irregular, frequently assuming the form of a stellate 

 .tissue. 



In the Skate, then, the follicle is an involution of the derm, the 

 papilla is a process of it, and the epithelium between the two becomes 

 metamorphosed sometimes into a peculiar stellate tissue. The same 

 essential relations prevail as before. 



In Man, some confusion has prevailed with regard to the homology 

 of the various component parts of the tooth sac, though they might be 

 readily enough deduced from the mode of development of the sac ; 

 however, it is, I think, not at all difficult to obtain perfect demonstra- 

 tion upon this subject. 



If a young tooth capsule be opened (say of a fcetus at the seventh 

 month), whatever care may be exercised, it will always be found 

 (Hunter, Bichat) that a space filled with a fluid exists between the 

 inner surface of the capsule and the outer surface of the pulp — the two 

 .are perfectly free from all adherence to one another — the only substance 

 between them, besides the fluid, being a more or less abundant whitish 

 matter which sometimes adheres to the one and sometimes to the 

 other {see Goodsir, /. c). 



If the tooth be very young, a structureless membrane, the m. 

 preformativa of Raschkow (the basement membrane of Bowman), 

 may be traced over the whole surface of the pulp, or if calcific 

 deposition have already commenced, it may be found readily enough 

 at any rate in the lower unossified part ; and it is not at all difficult to 

 trace this in perfect continuity on the walls of the capsule — in fact 

 into its basement membrane. The best way of seeing this is by 

 detaching the whole sac from its alveolus, and then, laying it carefully 

 open in a watch-glass, turn the capsule carefully back, transfer the 

 whole to a glass plate, and cover it with a piece of thin glass. The 

 continuity of the basement membrane of the pulp with that of the 

 capsule is now evident enough under the microscope. 



The wall of the capsule is often folded, and sometimes I have 

 _noticed villous processes, such as those described as vascular by Dr. 



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