THE TEETH OF MARSUPIAL ANIMALS. 
409 
crown proceed upwards, then in a large curve bend outwards, and when within the 
x^o^th of an inch of the enamel give off an abundance of short fine tubules, and 
when so doing turn upwards, having but few previously, and none at all until within 
half-way of the enamel. On entering the enamel they again make a small curve 
downwards, give off occasional branches, and make numerous short deflections 
downwards, and after advancing through about two-thirds of the thickness of the 
enamel are lost, fig. 8. 
The tubes at the pulp-cavity measure about io,ooo4 h of an inch in diameter, and 
on entering the enamel ^6 Qoo th of an inch ; when within the enamel they increase to 
about the 20 , 000 th, and gradually diminish till they become invisible, or are lost in 
small cells. On the lingual surface of the tooth, the tubes in this, as in many other 
marsupial teeth, commence by small cells. 
The dentinal tubes of the fangs are lost in the cement, between which and the den- 
tine there is no strongly-marked line of demarcation. The cemental cells are large, 
elongated in figure, and have many and large tubules. 
In the molar teeth of Dasyurus macrourus the dentinal tubes branch more sparingly, 
and on entering the enamel are not subject to the same degree of deflection, though 
possessed of the same general character as those seen in the D. ursinus ; neither do 
they suffer any enlargement in the first part of their course, as is common in the last- 
mentioned tooth, fig. 9. 
The cemental cells are more simple in form, and the dentine and cement are sepa- 
rated by a well-marked line of junction, except at the apex of the fang, where the 
cement is reflected for a short distance up the canal. 
In the canine teeth of this animal a considerable portion of the lower end of the 
fang is made up of cement. In the concave lingual surface of the crown the enamel 
is thin, and the tubes frequently commence in small cells. The dentinal tubes give 
off small branches during the greater part of their course, and when close to the 
enamel occasionally turn upward and dilate into elongated cells. 
Thylacinus cynocephalus . — The teeth of this creature have a strong family resem- 
blance to those of the Dasyuri last described. There are however minute points of 
difference. The dentinal tubes, in addition to giving off minute short pilose branches, 
on nearing the enamel divide into several large branches, fig. 10 A. They are like- 
wise more disposed to dilate on entering the enamel, though many proceed without 
marked increase of size. Then, again, the tubes are lost by the time they have 
gained the inner fifth of the whole thickness of the enamel ; and the enamel fibres are 
more distinctly marked than in either of the preceding species excepting the Wombat, 
thereby approaching in structure to the teeth of the ordinary carnivora, fig. 10. The 
dentinal tubes, on leaving the pulp-cavity to proceed towards the coronal surface, 
have a diameter of about the xoTo^th of an inch ; on reaching the periphery the 
ill i'll® first part of their course in the enamel the ~ 2 b,Voo th- Those 
destined for the upper part of the crown advance upwards, and then make one large 
