512 CARNIVORES. 



cement, and the pulp-cavity is generally closed by an unusual quantity 

 of the osteo-dentine. The calcigerous tubes in the dentine of the 

 Seal's molar describe very strong and irregular curves on leaving 

 the pulp-cavity ; but, when within a third of the distance to the outer 

 surface, they fall into more parallel and regular undulations ; they 

 are ig^th of an inch in diameter, and the interspace between two 

 tubes is about -^th of an inch in width. The tubes dichotomise less 

 frequently and less regularly than in the teeth of the Dog or Hyaena, 

 but send from both sides extremely numerous short branches, 

 which bend almost transversely across the interspaces, and the sub- 

 branches are continually sent off in greater abundance along lines 

 parallel with the outer contour of the tooth, giving the appearance of 

 opake strise or concentric layers to polished sections of the dentine. 

 The calcigerous tubes resolve themselves at their extremities into 

 rich tufts of curved branches which terminate in a layer of minute 

 cells at the crown, and in the root, communicate with the radiated 

 cells of the cement. 



In the molar teeth of the Otaria jubata the tubes proceeding in 

 the long axis of the crown are pretty parallel on the peripheral half 

 of the dentine ; towards the side of the crown they proceed in more 

 zigzag, almost angular curves and appear to cross each other, 

 conspicuous branches being continued from the angles : the inter- 

 spaces of the tubes were about gwoth of an inch in width. The den- 

 tinal cells are more numerous and less regular than in the teeth of 

 the ordinary Carnivora, and their contour is more obscured by the 

 deeper curves and more numerous branches of the dentinal tubes. 



The enamel of the teeth of the Carnivora is extremely dense and 

 brittle, it consists of fibres similar to those in the Human teeth, but 

 relatively smaller, as for example, in the large canines of the Tiger, 

 and the molars of the Hyaena. The transverse striae, moreover, are 

 less distinct. 



In the molar of the Otaria the enamel fibres were very distinct, 

 placed at right angles to the plane of the crown, and less curved than 

 in Man or the Quadrumana. Instead of the transverse striae they 

 presented a minute granular structure. (1) 



(1) Retzius failed to detect any true enamel in the teeth of the Phoca anellata. 



