CETACEANS. 363 



they are about gjo^th of a line in diameter, generally of an oval 

 form, but with very irregular outlines ; the tubes radiating from 

 the cells are wider than usual at their commencement, but soon 

 divide and sub-divide, forming rich reticulations on the interspaces 

 and communicating with the branches of parallel larger tubes. 

 These are placed, as in the Dugong, perpendicularly to the super- 

 ficies of the tooth, but are less regularly arranged than the 

 calcigerous tubes of the dentine, with which, however, they form 

 numerous continuations. There is a greater proportion of the 

 cement at the isthmus of the bilobed base of the crown than at its 

 circumference. 



The dentine consists of fine calcigerous tubes, radiating in the 

 section examined from two centres, one in each lobe, without any 

 intermixture of medullary tubes. The breadth of the calcigerous 

 tubes in tbe Zeuglodon is equal to one-eighth of the diameter of 

 an ordinary human blood-disk or globule ; they present a regular 

 undulating course, and like the calcigerous tubes of the Cetacea 

 exhibit plainly the primary dichotomous bifurcations, and the 

 subordinate lateral branches, which are given off at acute angles. 

 Upon the whole the microscopic characters of the texture of 

 the teeth of the Zeuglodon are strictly of a mammiferous character, 

 and its minor modifications agree with those in the Cetacea. 



If the crowns of the teeth be at no period, which is unlikely, 

 tipped with enamel, yet the presence of fangs, proving their restricted 

 time of growth, shows the Zeuglodon not to have been a member of 

 the order Bruta, and the microscopic structure displays no vascular 

 dentine which enters so largely into the composition of the teeth 

 of the gigantic extinct Sloths. The outer cement is much thinner 

 in proportion to the dentine than in the Cachalot, and there is 

 a much less quantity of the irregularly ossified pulp in the centre ; 

 the teeth, moreover, were developed in both the upper and lower jaws 

 of the Zeuglodon. The two fangs distinguish in a marked degree 

 the Zeuglodon from any of the true Cetacea, among which, however, 

 we have seen that the Platanista makes an approach to this structure 

 in the hindmost teeth. The obtusely serrated margins of the crowns 

 also form a peculiar character in the present order, but which is 



