346 CETACEANS. 



of the Bruta, since the teeth are all of a more or less simple, conical 

 form, and none of them present flat or ridged crowns like true 

 molars : nevertheless we here first, in the ascensive survey of 

 Mammalian dentition, find enamel entering into the composition 

 of the teeth, the sharp crowns of those of the predaceous Dolphins 

 being tipped or sheathed by this hard substance. 



The main anomaly of the dental system in the family Balcsnidce has 

 already been treated of in the chapter on Horny teeth. But the great 

 Whales, before they acquire their peculiar array of baleen plates, 

 manifest in their foetal age a transitory condition, a true dental 

 system, which, though abortive and functionless, beautifully typifies 

 that which is normal and persistent in the majority of the order. 



In an open groove, which extends along the alveolar border of 

 both the upper and the lower jaws, there is a series of minute, conical, 

 acute, or obtuse denticles, with hollow bases inclosing the uncal- 

 cified remains of a Vciscular pulp. These were first noticed by the 

 philosophical anatomist, Geoffrey St. Hilaire, and have subsequently 

 been described and figured by Prof. Eschricht. The subject ex- 

 amined by the latter Author was the foetus of a Balcenoptera, the 

 jaws of which were about four inches in length. The unclosed 

 alveolar groove of the upper jaw contained twenty-eight denticles(l), 

 that of the lower jaw forty-two. The anterior denticles in both 

 jaws were the smallest ; but they increase in size more gradually, 

 and maintain a greater regularity of form in the lower jaw, where 

 they are also most numerous, and in which the typical dentition 

 of the carnivorous Cetaceans first manifests its plenary develop- 

 ment in the great Cachalot. In the upper jaw of the foetal Whale 

 some of the denticles are double, two adhering together side by 

 side(2), and they offer in their varying extent of confluence, no unapt 

 resemblance to the stages of the fissiparous multiplication of an 

 infusorial Monad : there can be little doubt, indeed, that these 

 literally ' double-teeth' have resulted from a spontaneous fission 

 of the primordial pulp-cell; the divisions of which growing to a 

 certain size, have again coalesced in the progress of their calcification 

 like the two primitively detached summits of the Ornithorhynchus's 

 grinder. We cannot avoid recognising in these bicuspid denticles 



(I) PI. 90, fig. 1. (2) lb. figs. 5 and 6. 



