12 
EDWARD J3. POULTON. 
part of the opposite maxilla, aud the detached fragment of 
tissue, were cut into consecutive transverse sections; hut al- 
though some appearances seemed to point to the existence of 
such a tooth, the condition of the specimens prevented any 
certainty on the point. Thus the teeth had been greatly in- 
jured by the partial cleaning of one specimen, and the other 
was by no means complete. These conditions did not, however, 
affect the histological part of the investigation. 
Since the account was sent to the Royal Society I have 
been greatly interested to find an additional tooth, in a very 
early stage, immediately behind and to the inner side of the 
posterior tooth, as previously described, in both upper and 
lower jaws (see PI. Ill, fig. 7 x 50). Hence there are 
traces of four teeth in the upper jaw and probably the same 
number below. 
Position of the Teeth. — These teeth are placed in an 
antero-posteriorly directed row, exactly as Tomes describes 
in the development of the typical mammalian tooth, “ in a 
widely open gutter of hone,” and the condition of my material 
indicated that “ if at this stage the gum be stripped off from 
the jaws the developing tooth capsules are torn off with the 
gum” ('Dental Anatomy,’ 187G, p. 134). In the lower jaw 
no bone had been developed between the teeth and the very 
large inferior dental nerve which therefore passes along the 
bottom of the dental furrow ; and the same fact holds as 
regards the superior maxillary division of the fifth nerve aud 
the upper teeth. The posterior upper teeth are similarly un- 
separated by bone from the closely adjacent muscular tissue 
lying between the zygoma and the skull. The teeth of 
both jaws lie in the groove which subsequently holds the 
posterior horny plates which subserve the function of mastica- 
tion. At first, when I had only examined Dr. Parker’s sections 
of the skull, I did not think, for reasons which will be given 
below, that the teeth exactly corresponded to the future site 
of the plates ; but this became certain when I carefully com- 
pared the cleaned skull and inferior maxilla with the sections 
of both upper and lower teeth, and with the dissected pre- 
