364 HALICORE. 



present in the dentition of some species of seal. (1) In the so-called 

 herbivorous Cetacea, whose dentition will next be described, the 

 two-fanged structure is fully established in the Manatee, whilst in 

 the Dugong we shall find the near resemblance to the Zeuglodon 

 in the composition and the intimate structure of the molar teeth. 

 The vertebrae of the Zeuglodon prove it, however, to be a true or carni- 

 vorous Cetacean ; its size is estimated at near seventy feet ; it accord- 

 ingly affords a very interesting addition to the history of the dental 

 system in the Cetaceous order, and approximates the typical group 

 by an additional step to the Dugongs and Manatees which are more 

 essentially related to the Pachyderms. 



147. Halicore. — Two marks of inferiority in the dental system of 

 the carnivorous Cetacea, which they have in common with many of the 

 order Bruta, viz : — uniformity of shape in the whole series of teeth, and 

 no succession and displacement by a second or permanent set, disap- 

 pear when we commence the examination of the dentition of those 

 apodal pachyderms which have been called the herbivorous Cetacea. 

 In the Dugong, {Halicore DugongJ for example, we find incisores dis- 

 tinguished by their configuration as well as position from the molares, 

 and the incisive tusk is deciduous, displaced vertically and succeeded 

 by a permanent tusk : both these characters are shown in PI. 92. 



Of the incisors of the Dugong only the superior ones project 

 from the gum in the male sex, and neither upper nor lower ones 

 are visible in the female (2). The superior incisors are two in number 

 in both sexes ; in the male they are moderately long, subtriedral, 

 slightly and equally curved, of the same diameter from the base, 

 which is deeply excavated to the apex, which is obliquely bevelled 

 off to a sharp edge, like the scalpriform teeth of the Rodentia. 

 The form and extent of the persistent pulp-cavity of this tooth are 

 shewn in the figure of its longitudinal section, two-thirds the 

 natural size, in PI. 93, fig. 4. Only the extremity of this tusk 

 projects from the jaw, at least seven-eighths of its extent being 

 lodged in the socket, the parieties of which are entire and the 



(1) A fossil carnivorous Cetacean with serrated teeth has been indicated by M. Grateloup, 

 under the hybrid name of ' Squalodon,' in Leonhard and Bronn, Jahrbuch fiir Minera- 

 logie, 1841, p. 830. 



(2) Proceedings of the Zool. Society, 1838, p. 41. 



