THE TEETH. 105 



Beneath the cement the intercommunication of interglobu- 

 lar spaces and bone-lacunae is well shown. The interglobular 

 substance is apt to be present in layers ; the lines which are 

 then called the incremental lines of Salter, are supposed to 

 show that there has been growth by successive stages. The 

 lines of Schreger (Fig. 38, 2) are also waving parallel lines ; they 

 are thought to be due to the curvature of a series of adjacent 

 fibres. In some instances vascular channels have been found 

 in the dentine, which has acquired the name osteo or vaso- 

 dentine. In pathological conditions masses have also been 

 found containing bone-lacurise. They have been called odonto- 

 mata by Yirchow. 



The cement is true bone-tissue, containing lacunae and 

 canaliculi, and in them the bone-corpuscles with their pro- 

 cesses. The matrix is also subdivided into lamellae. The peri- 

 osteum of the gum dipping down into the bony socket from 

 the surface of the gum forms a coating over the cement. Oc- 

 casionally Haversian canals and blood-vessels are seen where 

 the cement is thick (Salter). Sharpey' s fibres may also be seen, 

 according to Waldeyer. 



The pulp is a substance that belongs to the connective- 

 tissue series. Adjoining the dentine are two layers of corpus- 

 cles. The nearest are long cylindrical bodies whose oval nuclei 

 are distant from the dentine. Wedged in between them, and 

 forming a layer intermediate between them and the pulp, are 

 peculiar branched corpuscles of a spindle or pyramidal shape. 

 According to Klein, these latter send processes into the den- 

 tinal tubules, while, according to Waldeyer and Boll the odon- 

 toblasts send the fibres, and are also connected to one another 

 by lateral processes. The pulp tissue is very rich in non- 

 medullated nerves ; their prolongations penetrate between the 

 odontoblasts, but it is a matter of question whether they enter 

 the dentinal canals. 



Capillaries are abundant and form close networks in the 

 pulp. The lymphatics are said to accompany the blood-vessels 

 and to be surrounded by endothelial sheaths. 



Development of t?ie teeth. Waldeyer, whose views on the 

 teeth are the most complete and satisfactory extant, makes the 

 following succinct statement : 



"The anatomical model of a tooth of a vertebrate animal 

 is a large papilla of the mouth or of the pharyngeal mucous 



