272 DR. H. W. MARETT TIMS ON 
fact of some importance, and to which I shall again have to 
refer. In quite the posterior part, the tooth forms a solid 
transverse mass with a blunted apex, slightly more prominent 
on the outer side. The accompanying illustrations will, perhaps, 
render this description more intelligible (fig. 4). 
I would here add that I have found a similar condition in 
m.1 of the rat, the only exception being that in this animal 
there is the further complication of a channel of communication 
between the central cavity and the external surface of the tooth, 
which cuts off the apex of the external cone from its basal 
attachment. As the apex of this tooth in the guinea-pig now 
nearly reaches the surface of the gum, its epithelial connection 
is broken up, no labial or lingual downgrowths of the dental 
lamina nor any appearance of a “concentric body” being 
visible. 
The fourth cheek-tooth is almost identical in pattern with 
that of the third as seen in Stage 2, and the description afore 
given would apply equally to the tooth under consideration; 
the only addition which it is necessary to record, is the presence 
of a relatively large tubercle to the outer side of the main cone 
in the posterior part of the tooth. It attains to such a size, that 
were the cusps not carefully followed throughout, it might easily 
be mistaken for the main external cone with a slightly more 
prominent internal cone. 
The fifth cheek-tooth is deeply situated, its enamel organ 
being in the bell-shaped stage. Between this and the tooth in 
front is another of the “ concentric bodies” to which reference 
has been made. Its exact relationship to the tooth bebind 
cannot be established, owing to the dental lamina being difficult 
to follow. It can, however, be seen to lie well to the labial side 
of the teeth and between them. 
Stage 4: (Fetal) (fig.5). Circumferential head-length.. 4 cm. 
p body-length.. 10cm. 
The jaws were examined by clarifying in oil of cloves. The 
condition is interesting as the deciduous tooth is about to be 
shed, having entirely disappeared in the subsequent stage ; it is 
therefore lost either just after birth, or, as is more generally 
stated, at quite the late period of intra-uterine life. All five teeth 
are well-calcified, the deciduous tooth lying between the crown 
of the anterior permanent tooth and the free margin of the 
