324 ARMADILLOS. 



any other species of the order Brida, but, as in all that order 

 provided with teeth, they are wholly devoid of enamel : it is not 

 true, however, that they have no cement, as Retzius believed. 

 They consist, in both existing and extinct Armadillos, of three 

 distinct substances, of which the unvascular dentine is present in 

 greatest proportion, and forms the main body of the tooth : but 

 it includes a small central axis of vascular dentine, and is sur- 

 rounded by an extremely thin coating of cement. 



The calcigerous tubes of the dentine are continued from the 

 vascular or Haversian canals of the central bone : in the Dasypus 

 sex-cinctus{] ) they present strong curvatures at their commencement, 

 except the few which arise from the summit of the central axis : 

 these ascend vertically to the grinding surface ; the surrounding 

 tubes rapidly diverge like the outer streams of a fountain ; and 

 throughout the rest of the body of the tooth the calcigerous 

 tubes bend outwards, and direct their course at right angles to 

 the axis of the tooth, but with a slight convexity directed towards 

 the grinding surface. The diameter of the calcigerous tube, where 

 the parallel course and moderate and regular curve begins, is 

 ^u'^h of an inch ; the interspace of two tubes equals four of their 

 diameters. The interstitial branches are not easy of detection, but 

 the terminal ones are sufficiently obvious : they are numerous, often 

 irregularly curved ; many appear to anastomose, either directly or by 

 intermediate cells, close to the cement (2) ; others are directly con- 

 tinued into that substance, and terminate in its cells. 



The central axis of the solid part of the tooth is occupied, as 

 already stated, by a hard substance, closely resembling bone, (3) in 

 which the last traces of the dentinal pulp appear as the vascular 

 occupants of the medullary canals : these canals are few in num- 

 ber, have not a regular or parallel arrangement, and do not an- 

 astomose by loops : some of them are continued, along with short 

 processes of the osseous substance a little way into the dentine : 

 a rich pencil or brush of calcigerous tubes radiates in strong irregular 

 curves from the obtuse ends of these processes, before falling into 

 the common parallel course. 



(1) PI. 85, fig. 4, b. (2) lb. fig. 4, c. (3) lb. fig, 4, a. 



