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ME. C. S. TOMES ON THE DEVELOPMENT OF THE TEETH 
Anguis fragilis and Lacerta viridis . — The descriptions of these two forms may be 
most conveniently taken together, as no differences of importance have to be recorded 
between them. The area of tooth-development exists in them as a sharply defined 
region, bounded on its inner side by connective tissue, just as in the newt and the 
frog ; but although it is not restricted by extraneous causes, such as the antagonism 
of the upper and lower jaws, it nevertheless is not widely extended as in the newt, but 
contains only one advanced tooth-sac at one time (Plate 47. figs. 16, 17, 18). The 
tooth-sac acquires a more definite connective-tissue investment than was the case in the 
frog (fig. 19 and the right-hand lower corner of fig. 22); but this investment, so far as 
it can be said to be such, seems to be mainly due to the displacement of a loose connective 
tissue in front of the growing tooth-germ, and it plays no active part in the formation 
of the tooth. The base of the dentine-papilla also is not so sharply cut off as in the 
newt and frog, but it shows an appearance of prolongation from its base upwards 
around the end of the enamel-organ (fig. 19). 
The enamel-germ appears to be given off from that of the preceding tooth-sac (fig. 19) ; 
at least a process is very often discoverable at the side of this latter, although the con- 
nexion with the oral epithelium is not lost and appears to be tolerably direct (see figs. 
18 & 16) : I am inclined to think that the enamel-germs do not arise from the oral epi- 
thelium quite de now for each tooth-sac, but that they may be justly described as succes- 
sive branches of a common stem. An early stage of a tooth-sac is represented in fig. 20, 
in which the dentine-papilla is seen to be distinct in its origin from the enamel-organ, 
but to be a portion of the tissue into which this latter dips down, and to be quite con- 
tinuous with the connective tissue which forms an adventitious investment to the whole 
sac and to the elongated neck of epithelial cells above it. 
The cells which lie upon its surface become elongated to form an odontoblast layer 
or membrana eboris, and the whole dentine-papilla speedily becomes differentiated 
from the tissue around from which it took its origin. 
The enamel-organ presents no special peculiarity ; the inner layer of cells is distinctly 
columnar, and the outer more nearly spherical, the enamel-organ consisting exclusively 
of these two layers with no intermediate structure (figs. 19, 21). 
When a cap of dentine, tipped slightly with enamel, has been formed, the odonto- 
the form of a papilla developed from the bottom and toward the outer side of a small fissure in the mucous 
membrane or germ that fills up the shallow groove at the inner side of the alveolar parapet and its adherent 
teeth ; the papilla is soon enveloped by a capsular process of the surrounding membrane ; there is a small 
enamel pulp developed from the capsule opposite to the apex of the tooth ; the deposition of the earthy salts in 
this mould is accompanied by ossification of the capsule, which afterwards proceeds pari passu with the calci- 
fication of the dental papilla or pulp ; so that, with the exception of its base, the surface of the uncalcified part 
of the pulp alone remains normally unadherent to the capsule.” That there is no papillary stage was pointed 
out by Prof. Huxley (Joe. cit.), who, however, did not trace out all the details of the process, and makes no 
particular mention of the epithelial inflections ; as to the latter part of Prof, Owex’s description, I have never 
observed any thing which could be called ossification of the capsule, if, indeed, there he such a structure as 
the capsule at all in the sense in which he employs it. 
