HARDWICKE'S SCIENCE-GOSSIP. 



75 



In the new tooth the canals in its base are quite as 

 large as those in Cteuoptychius, but they become 

 rapidly smaller as they proceed towards the denticu- 

 lar surface; the larger canals branch and anastomose 

 freely, but less so when they become smaller : they 

 all give off tubules, but very sparsely, with the 

 exception of those near the first and second denticles, 

 where the tubules are rather numerous (figs. 58, 59), 



are merely sharp points. The first four denticles 

 have from two to three small points on their free 

 surface: these are seen in figs. 58 and 59 to be com- 

 posed purely of ganoine, each point of ganoine being 

 continuous with its neighbour of the same denticle ; 

 but the enamel of one denticle is not continuous 

 with that of the denticle next to it, except between 

 the second and third. The middle points or denticles 



Fig. 58. Vertical Section of Fig. 66, magnifled 20 diameters. 



and being the largest they are the only ones seen 

 under a power of 20 diameters : the finest tubules 

 require a power of about 400 diameters to resolve 

 them. The calcigerous tubules are very fine, the 

 largest measuring 

 beins 



O 10 



in. 



15000 1^ 



seldom, and do not anastomose 



in diameter, the average 



they branch dichotomously, but 



The tubules in 



the body of the tooth run at right angles to the 



are also tipped with this fish-enamel; but beyond 

 these the points are composed purely of dentine, the 

 enamel, it may be, having been worn off. The fish- 

 enamel, or ganoine, is permeated by calcigerous tubes, 

 which are continuous with those of the dentine; they 

 are similar in size to the dentinal tubules, but ap- 

 pear larger, and therefore more distinct, by force of 

 contrast with the clear substance in which they 



Fig. 59. Vertical Section of Tootli (fig. 56) continued, x 20. 



canal from which they arise, while the denticular 

 tubules proceed parallel with the axis of the tooth, 

 with the exception of those in the first denticle, at 

 the base of which they run at right angles to the 

 axis, becoming vertical towards the apex (fig. 60). 

 The denticles, as I have already said, rapidly de- 

 crease in sizCj from one side to the other, till they 



ramify (fig. 60). The largest point of enamel is only 

 3^0 of an inch in height. 



The second tooth was found in 1868, lying em- 

 bedded in shale, and is the only one in my possession. 

 On account of its shape being unlike that of auy 

 other tooth that 1 am acquainted with, a section was 

 made in order to ascertain its structure under the 



E 2 



