CETACEANS. 347 



the representatives of the molars of the gigantic extinct Cetacean, 

 called ' Zeuglodon,' and they also call to mind the similarly shaped 

 ultimate molar in the Dugong. 



These small teeth and their matrices entirely disappear before 

 birth : yet the foetal Whale comparatively long retains and palpably 

 exemplifies the earliest stage of dental development in the higher 

 Mammals, viz., the open fissure, which in these is so rapidly closed, 

 especially in the Human subject. But beyond this stage the true 

 dentition of the BalcBnidcB is not destined to proceed; and they 

 thus manifest, agreeably with the general laws of unity of organi- 

 zation, their closest relations to the typical characters of their order 

 at the early periods of development, divesting themselves of part 

 of the more general type, in order to assume their special and 

 distinctive characters, as they advance towards maturity. 



140. Hyperoodon. — The great bottle-nose or bident Whale 

 offers a beautiful transitional grade between the true Whales and 

 the typical Delphinidcs : the palate is beset with small, unequal, 

 pointed, callous processes, which Cuvier conjectures to be rudi- 

 mental baleen-plates ; whilst to balance, as it might seem, this 

 arrest of the development of the typical garniture of the Whale's 

 jaws, the foetal denticles do not all perish, but two or three 

 of the anterior pairs acquire a large size, as compared with their 

 transitory representatives in the BalcenidcB, and one of these pairs 

 is long retained in the lower jaw, though functionless and hidden 

 by the gum. 



These teeth are figured of the natural size at the extremity 

 of the lower jaw of an immature Hyperoodon, in PL 88, fig. 1. 

 They are conical, slightly curved, with an unusually sharp and 

 slender apex, tipped by enamel. Though loose in their sockets, 

 they project so little from them, and have such wide bases that 

 they are retained in situ, and do not fall out in the dried jaw : 

 two smaller cavities in front, and the remains of a larger socket 

 in the alveolar groove, behind the retained teeth, attest the former 

 presence of other teeth. 



141, Monodon. — In the Narwhal two of the primitive dental 

 germs at the fore part of the upper jaw, proceed in their deve- 



