40 CAETILAGE. BONE. TEETH. 



take their origin from minute cavities in the deeper 

 strata of the fundamental substance; these latter, 

 however, always communicate with the central cavity 

 o f the tooth (PL VIII. fig. II. 4). With a magni- 

 fying power of 350 to 400 diameters, the canals can 

 be seen to be sharply limited by two very fine but 

 distinct lines, to be slightly wavy or undulating in 

 their course, and to run, mainly, parallel to each 

 other. Their lateral branches can also be distin- 

 guished, radiating in every direction, anastomosing 

 with each other, and thus forming an universal net- 

 work, which permeates, everywhere, the fundamental 

 substance of the ivory. (PL VII. fig. III. 1, 2 ; PL 

 VIII. fig. II). 



At their origin the canals are larger than at their 

 termination, measuring, on an average, from r-nrcrth 

 to T^o-th of a line. Sometimes they present, in their 

 course, small spindle-shaped enlargements (PL VIII. 

 fig. II. 3), and they terminate, as a rule, in irregularly 

 shaped cavities which are the interspaces between 

 minute glob . ar masses of the fundamental substance 

 (PL VIII. ng. II. 5). It is to be noticed that these 

 inter-globular spaces, as they have been designated, 

 communicate freely with the bone-cells of the cemen- 

 tum, to which, in fact, they bear no little resem- 

 blance. 



Enamel. The 'enamel forms a hard and homogeneous lamina 

 moulded accurately upon the surface of the crown of 

 the tooth, and terminating, at its neck, by a thin 

 edge, which seems to insinuate itself between the 

 ivory and the terminal margin of the cementum. It 

 is composed exclusively of five or six-sided prisms, 



