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On the Teeth of the Ox, Sheep, and Pig, 
towards the periphery of the structure. In fig. 6 we have a view 
of these tubes magnified 400 diameters, which, like many other 
illustrations contained in these pages, has been taken from the 
Fig. 6 * 
tooth of a sheep. In fig. 7, A represents the tubes, similarly 
magnified, as imbedded in the intertubular substance, and cut 
transversely ; and, b, when they are cut obliquely. Examined 
with transmitted light, these tubes always appear of a dark colour, 
a circumstance which has been variously accounted for. Some 
suppose that it depends merely on their walls being more opaque 
than the surrounding intertubular substance. 
Fig. 7 A.f Fig. 7 B.I 
In this particular these dentinal tubes agree with hair, which 
has usually a dark central line running from the root to the point, 
and marking the seat of its inner tubular or cellular portion. It 
should be observed, however, that all the hairs even of the same 
animal are not cellular. Some are without this structure, and as 
such they are naturally transparent ; while others possessing it 
are on the conti-ary opaque. These latter named hairs can how- 
ever be rendered transparent by immersion in fluids which will 
penetrate the walls of the cells composing their tubular portion. 
The true tubular character of dentine is likewise shown by im- 
* Fig. 6. Dentinal tubes ending in lacunae, sheep, magnified 400 diameters, 
t Fig. 7 A. Transverse section of dentine magnified 400 diameters, showing the 
tubes and tlie intertubular structure. After Todd and Bowman, slightly modified. 
X B. Oblique sectiou of dentinal tubes magnified 400 diameters. After Hassall. 
