292 CROCODILIANS. 



cated by the dotted line in plate 75, fig. I), and is commonly either 

 perforated or notched at its concave or inner side. 



The calcigerous tubes in the crown of a fully- developed tooth 

 form short curvatures at their commencement at the surface of the 

 pulp -cavity, and then proceed nearly straight to the periphery of 

 the crown ; they very soon bifurcate, the divisions slightly diverging ; 

 then continuing their course with gentle parallel undulations, they sub- 

 divide near the enamel, and terminate in fine and irregular branches, 

 which anastomose generally by the medium of cells. 



The calcigerous tubes send off from both sides, throughout their 

 progress, minute branches into the intervening substance, and ter- 

 minate in the dentinal or calcigerous cells. These cells are subhex- 

 agonal, about ^-Jijth of an inch in diameter, and are traversed by from 

 ten to fourteen of the dentinal tubes : they are usually arranged in 

 planes parallel with the periphery of the crown, near which they 

 are most conspicuous and towards which their best defined outline 

 is directed :(1) they combine with the parallel curvatures of the 

 calcigerous tubes to form the striae, visible in sections of the teeth 

 by the naked eye or a lower power, which cause the stratified 

 appearance of the dentine, as if it were composed of a succession 

 of superimposed cones. The diameter of the calcigerous tube 

 before the first bifurcation is la^ooth of an inch ; both the trunks 

 and bifurcations of the calcigerous tubes have interspaces equal to 

 four of their respective diameters. 



The enamel, viewed in a transverse section of the crown, pre- 

 sents some delicate striae parallel with its surface ; whilst the ap- 

 pearance of fibres, vertical to that surface, is only to be detected, and 

 there faintly, on the fractured edge. It is a very compact and dense 

 substance ; the dark brownish tint is strongly marked in the middle 

 of the enamel when viewed by transmitted light. 



The cells with which the fine calcigerous tubes of the basal 

 cement communicate are oblong, about gJuoth of an inch across their 

 long axis, which is transverse to that of the tooth ; the inter- 

 communicating tubes, which radiate from the cells, giving them a 

 stellate figure. 



(1) " Report of British Association," 1838, p. 144. 



