NO. 1699. ON EDESTUS AND RELATED GENERA— HAY. 51 



have been cut away the hinien appears. As the surfaces of the organ 

 are approached, the filling of the channels with pja-ite becomes more 

 complete. In fig. 1 of pi. 13 and also in fig. 2, in order to bring out 

 the structure, the lumina of the vessels are represented as black. 

 The light spaces between the network of black lines represent the 

 dentine substance. 



Examination of the section shows that the longitudinal canals, 

 large and small, are abundantly connected by anastomosis, so that 

 the vascular apparatus formed a dense network. In the lower por- 

 tion of the section, that corresponding to the root of the tooth, many 

 of the larger capillary canals approach the surface, and probably 

 some of them passed out into the surrounding tissues. Fig. 2 on 

 pi. 13 represents a median sagittal section of another small segment 

 of Edestus. This is taken in front of the tooth and includes no part 

 of it. Most of the vascular canals run longitudinally. The main 

 longitudinal canal is seen near the bottom of the section. As seen 

 in favorable situations, fine branching lines run away from the 

 borders of the capillary canals. These lines are regarded as marking 

 the dentinal tubes. Often, especially near the capillaries (pi. 13, 

 fig. 3, taken from near the anterior border of a tooth) , they have 

 the lumen filled with pyrite, and then they resemble the canaliculse 

 of bone. Where not indicated by pyrite filling, the tubes may never- 

 theless often be traced out under the microscope, and they constitute 

 a network of fine lines in the dentine. Nowhere does there appear 

 to be any layer of dentine made up of tubes running parallel with 

 one another. 



The layer of enamel is so deeply stained with pyrite that few 

 observations can be made on it. In one spot it is sufficiently thin 

 and translucent to allow it to be seen that the enamel is penetrated 

 b}^ nearly parallel black lines, which stand at right angles with the 

 outer surface of the tooth, but do not quite reach this surface. This 

 is to be taken as that variety of enamel described by Tomes as being 

 penetrated by dentinal tubes." 



KariDinsky * has noted the resemblances between the teeth of Hell- 

 coprion and those of various sharks, living and extinct. The present 

 writer has wished to compare Edestus with the spines of fossil sharks, 

 and has accordingly made sections of a fragment of the spine of 

 Ctenaccmthus varians (pi. 13, figs. 4, 5). Although differences be- 

 tween this genus and Edestus may be observed, the writer regards 

 the structure of the two as being essentially the same. In the speci- 

 men of Ctenaennfhits nearly all the capillary vessels are probably 

 filled with limonite, while few of the dentinal tubes are thus filled. 



"Manual Dental Anat, 6th ed., p. 30. 



* Verhandl, russ.-kais. min. Gesellsch. St. Petersb., 2d ser., vol. 26, 1898, p. 420. 



