558 
MR. TOMES ON THE STRUCTURE OF 
appearance of-being in pairs, the fibres of which proceed obliquely outwards from a 
central line common to the two, as shown in fig. 46. In the outer division of the 
tissue the component fibres are so intimately united, that in places only can their 
course be traced. In a longitudinal section the lamellse leave the dentine at an angle 
of 70°, which is reduced to 30° in the outer part of this substance. The layers have 
a thiekness of about the 700th of an inch, and the component fibres a diameter of 
the 7500th of an inch. The whole thickness of the enamel amounts to the 79th of 
an inch, of which yflhs is lamelliform. 
In a transverse section of an upper incisor, the enamel fibres are seen to make one 
bold sigmoid curve in the lamelliform portion of the tissue. In fig. 45, a layer of 
fibres is shown with as much of the one immediately beneath as could be seen without 
shifting the focus of the instrument. 
The enamel of the molar teeth exhibits much the same structural appearance as 
that of the incisors, excepting that the cells which occupy the inner part of the tissue 
in the latter teeth, are absent in these. 
Brathyergus maritimus, Gml. (Zoological Society). — This animal has been placed 
by Mr. Waterhouse in a section immediately preceding Hystricidce*. The teeth are 
however Hystricine in structural character, and might be described either in this 
place or at the beginning of the family. 
The dentine of the anterior parts of the tooth is bordered by a narrow layer of cells. 
The dentinal tubes have small hair-like branches through the whole of their course. 
In a longitudinal section of an upper incisor confluent layers of enamel fibres 
leave the surface of the dentine at an angle of 50°, and after extending about the 
210th of an inch, are insensibly lost in the parallel arrangement of the fibres in the 
unusually thick external division of the tissue, which in this tooth amounts to the 
120th of an inch in thickness, as shown in fig. 47- The tissue is dotted near the 
surface with minute cells. A transverse section is not altogether unlike a corre- 
sponding one from the incisor of the Capyhara. 
Pedetes Cafer (Pall.). — This animal is placed by Mr. Waterhouse in the family 
Muridae, section Dipodina. The dental tissues of the incisor teeth have the Hystricine 
character strongly marked, while those of the molars are intermediate between the 
Hystricidee and Leporidse. The true position of the tissues in this family can only be 
determined after the majority of the species have been examined, which in itself will 
be a work of some labour, apart from the difficulty of obtaining authentic specimens. 
In the absence of correct information of its position, I have as a matter of convenience 
placed my description at the end of the Hystricine group. 
In the incisors the dentine has several minor points of peeuliarity. The pulp-cavity 
in a transverse section of a lower incisor approaches a triangular figure with the 
angles extended and rounded at their extremities, two of which are directed to the 
lateral anterior angles of the tooth, and the third extends in the median line into the 
* Johnston’s Physical Atlas. 
