SECT. I37.] 



THE TEETH. 



193 



Fig. 122. 



more or less parallel to the circumference of the crown, and varying in dis- 

 tance from each other, though some- 

 times close together ; in transverse 

 sections they appear as rings, and 

 are especially distinct in the crown. 

 These contour-li/ics, as they are called 

 by Omen, are the expression of the 

 stratified depositions of the dentine. 

 In animals, they are occasionally very 

 beautiful, particularly in the Cetacea 

 and Pachydermata (Zeuglodon, Bugong, 

 Elephant), and also in the Walrus. 

 Here, as also in fossil teeth, a breaking 

 up of the ivory into lamellae {Omen) is 

 very frequently observed, indications 

 of which are also found in fresh hu- 

 man teeth, and in tooth-cartilage. 



At the crown, the dental canals not 

 unfrequently pass for some distance 

 into the enamel, and occasionally en- 

 large so as to form wider cavities (fig. 

 125), which, perhaps, are to be regarded 

 as being more of a pathological nature. 

 Similar not quite normal formations are 

 the interglobular spaces in the dentine 

 itself. Czermak designates with this 

 name very irregular cavities, which 

 are bounded by spherical projections 

 of the dentine, and which are situ- 

 ated at the extremities of the contour- 

 lines. The spaces themselves are 

 sometimes very large, traversing nu- 

 merous dentinal canals, and interrupting 

 them in their course, sometimes very small, so that only some very few tubes 

 are involved by them. In the former case, their boundaries are distinctly 

 visible as spherical projections, of 0002"' to 0-012'" and more, which, being 

 penetrated by dentinal canals, and presenting quite the same appearance as 

 the dentine, are obviously merely portions of that substance, whilst in the 

 latter, these dentine-globules, as I will call them, are not always distinct. 

 This holds good especially for the smallest spaces, which, on account of their 

 jagged figure, and from the circumstance that the dentinal canals are in- 

 timately connected with them, might be held for bone-corpuscles in the 

 dentine, and have been so considered ; still, even in these, we are almost 

 always able, at least in the crown, to recognise their agreement with the 

 larger spaces. This is more difficult in the fangs, where smaller interglobular 

 spaces and globules form a granular layer (Tomes), which frequently looks 

 like a layer of small lacuna or simple granules. In the normal dentine, I 

 have but rarely observed true lacuna, and always only at the cement- 

 boundary ; on the other hand, interglobular spaces and dentine globules also 

 ur in the interior of the dentine of the fangs, and are especially beautiful 



Perpendicular section of the crown of an in- 

 cisor; magnified 7 times, a. Pulp-cavity; 6. 

 dentine; c. arcuate contour lines, with inter- 

 globular spaces ; d. cement ; e. enamel with 

 indication of the course of the fibres in different 

 directions ; //. colour lines of the enamel. From 

 man. 



