XXII.] 



TOOTH. 



253 



pulp-cavity and its contents. If the section passes directly through 

 the middle of the tooth, the orifice in the fang of the tooth may be 

 seen. 



(c.) (H) The dentinal tubules, not so distinct as in the dry tooth. 



r 







FIG. 242. Enamel 

 Prisms. 



FIG. 243. Their Hexa- 

 gonal Ends. 



FIG. 244. T.S. Fang of Tooth, a. Crusta pet- 

 rosa, with bone-corpuscles ; b. Dentinal 

 tubules ; c. Granular or interglobular 

 layer. 



If they are cut obliquely, they appear merely as tailed dots in a 

 homogeneous matrix. 



(d.) The pulp-cavity contains blood-vessels and fine connective 

 tissue, but next the dentine there is a layer of large cubical cells 

 odontoblasts which give off fine processes which enter the den- 

 tinal tubules the fibres of Tomes. They are best seen, however, 

 in a tooth which has not yet cut the gum. 



3. Development of Tooth. Without entering into all the 

 details of the development of the teeth, the following directions 

 will suffice as to the method of preparing sections so as to show the 

 various stages. What may be called the first stage that shown in 

 fig. 245 is to be obtained from the lower jaw of a sheep's embryo 

 7 cm. in length. At this stage only a very little bony matter exists. 

 Harden the whole jaw in corrosive sublimate and decalcify in dilute 

 hydrochloric acid. Stain in bulk in borax-carmine, embed in 

 paraffin, and make T.S. across both rami of the jaw and the tongue. 

 ( )r harden and decalcify at the same time the jaw of a fretal kitten 

 by placing small pieces containing embryonic teeth in Flemming's 

 fluid. This yields excellent results, the tissues are thereby suffi- 

 ciently differentiated and may be cut in paraffin. 



The second stage, fig. 246, is obtainable from the upper jaw of an 

 embryo sheep 1 5 cm. long. It is treated in the same way. 



The third stage, fig. 247, is obtained from the lower jaw of a dog 

 six days old or thereabout. 



