DEVELOPMENT OE THE TEETH OE EISHES. 
259 
connexion with the pulp and attachment to its base ’ as in man ; and the process seems 
to correspond with something more than the e first and transitory papillary stage of the 
development of the mammalian teeth.’ 
“ Each pulp is invested by a very distinct basement membrane, whose continuity with 
that of the mucous membrane of the follicle is very obvious. The epithelium of the 
follicle forms a thick layer, which sometimes, when the upper wall is stripped hack, 
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.” — “ On the Development of the Teeth,” 
Quart. Journ. Microsc. Science, 1853, p. 151. 
Any fortunate transverse section through the jaws of a rather young dogfish affords 
an excellent view of the relation of the various parts to one another. 
The dense gum or mucous membrane covering the convexity of the jaw is seen to be 
continuous with the softer and less fibrous tissue from which spring the dentine-papillae 
near to the base of the jaw (Plate 31*. fig. 1), and this again is continuous with the con- 
nective-tissue framework of the protecting “ thecal ” fold. The sheet of tissue from which, 
at the base of the jaw, young dentine-papillae originate becomes more fibrous as it passes 
upwards over the jaw, while those portions which intervene between the bases of the 
formative papillae have their fibres specially arranged with reference to the teeth, so as 
to form in some sort ligaments to secure them in place (see fig. 2), running from the 
base of one tooth to that of the next. 
The youngest dentine-papilla is a simple hemispherical eminence ; that next in age 
is conical, while above this point the characteristic form of the future tooth is more 
closely approached. 
In the youngest dentine-germs of the dogfish the cells near to the surface are larger 
than those more deeply situated, and measure about ^ of an inch in length ; in older 
germs the larger size and greater abundance of the cells upon the surface is noteworthy, 
but nothing at all comparable to the distinct odontoblast layer or membrana eboris, 
characteristic of the formative organs of hard unvascular dentine, is met with. 
It is not, however, so much in the dentine-papillae as in their epithelium that the chief 
interest lies, especially when the facts described by myself in a former communication 
upon the development of the teeth in Batrachia and Eeptiliaf are kept in view for the 
sake of comparison. 
Tracing the epithelium downwards from the exposed convex surface of the jaw (a, fig. 1) 
it is seen, opposite to the interspace between the third and fourth teeth, to leave the 
jaw and spring across to invest the thecal fold. In the specimen figured it has been 
t As well as the sequence of events occurring in the formation of mammalian germs as demonstrated by Prof. 
Koiixkee, loc. cit. 
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