300 
ME. C. S. TOMES ON THE STRUCTURE AND 
inclined, and finally (in the oldest teeth which have not as yet become attached to the 
jaw) it is nearly horizontal, so that the tooth lies parallel to the jaw, and is seen in the 
preparations in transverse section (7 in fig. 2). 
A ready clue to these peculiarities of position is furnished by the dilatability of a 
snake’s mouth ; it is essential that the successional tooth-germs should be disposed in 
the smallest possible space, while the recumbent position of the teeth which have 
attained to nearly their full length carries its own explanation upon the face of it. 
If the oral epithelium which is immediately to the inner side of the tooth in place 
(which, owing to the backward inclination of the teeth, can never be displayed in all 
its length in a section exactly transverse to the jaw) be traced downwards, it will be 
found to dip in deeply below the surface in the form of a distinctly circumscribed band, 
which does not pursue a perfectly straight course, but bends once or twice as it passes 
in (see e in figs. 2 & 3). 
This epithelial band reaches the region of the developing teeth, and there is more or 
less lost sight of; that is to say, although it reappears in the interspaces of the tooth- 
germs (see fig. 3), and doubtless is perfectly continuous from the surface to the deepest 
extremity of the area of tooth-formation, it cannot be seen in any one section in its 
whole course, as it is pushed out of the way and overlaid by the actively growing tooth- 
germs. In the interspace between each of these it can, however, always be seen 
distinctly ; and at the deepest or youngest end of the area it is seen in direct continuity 
with the enamel-organ of the youngest tooth -germ but one (fig. 4); while its blind 
extremity forms all that as yet exists of the youngest tooth-germ (see 1 in figs. 2 & 3). 
All the germs, with the exception only of the immediate successor to the tooth in 
place, are situated within a capsule or investment of connective tissue (fig. 3), forming 
an oblong or slightly pear-shaped area (its smaller end being downwards). This 
investment, common to a number of tooth-germs, is, so far as I know, peculiar to the 
Ophidia ; at least nothing like it is met in any of the Batrachia or Sauria which I have 
examined. 
When the tooth has attained to a considerable size, it escapes from the apex of this 
investment and passes towards the tooth already in place, which is then rapidly under- 
mined by absorption. When the tooth has fallen, the upper, and to some extent the 
inner, surface of the bone is exceedingly irregular, being everywhere roughened by the 
depressions characteristic of absorption (see the upper part of fig. 7). The tooth moves 
into position, carrying with it its capsule and all its contents. A very rapid formation of 
bone takes place, to which perhaps the capsule may contribute something ; the bulk of 
the new bone by which the tooth is attached, however, is formed outside and beneath 
the capsule, which in favourable sections may be distinctly seen passing directly across 
the base of the dentine, from one thin free edge to the other, even after a considerable 
portion of new bone has been formed. 
This new bone, formed altogether outside the tooth-capsule, is continued up on the 
outside of the dentine for a short distance (see figs. 6 & 7), and in this position has 
