Mr. G. R. Waterhouse on the Classification of Mammalia. 401 



which is much less contracted in front, and is produced poste- 

 riorly so as almost totally to conceal the cerebellum*. 



Taking the general form of the brain into consideration, the Pla- 

 cental Mammalia would appear divisible into two sections : first, 

 those in which the cerebrum is generallyof a rounded form, obtuse 

 in front and provided with distinct convolutions ; and secondly, 

 those in which the cerebrum is destitute of convolutions, or 

 nearly so, and usually contracted in front. The first division would 

 contain the Quadrumana, Carnivora, Cetacea, Pachydermata and 

 Ruminantia, and the second would contain the Cheiroptera, Insec- 

 tivora, Edentata and Rodentia, Again, the succession of the 

 orders of the first division as they are placed above would, in a 

 general way, tolerably well express the grade of development in 

 the parts of the brain of each, the proportion of the cerebrum to 

 the cerebellum, and of these to the spinal chord and medulla 

 oblongata. The medullary substance of the cerebrum is at first 

 deep, and the capacity of the lateral ventricles is small; the 

 optic lobes and the olfactory tubercles are also small in propor- 

 tion to the brain, whilst the corpus striatum, optic thalami and 

 corpora striata are well developed. The cerebellum is concealed^ 

 whilst in the last-mentioned of these orders (the Ruminantia) the 

 cerebellum is exposed ; the medulla oblongata and spinal chord 

 are proportionately large, and so are the optic lobes, and the 

 olfactory tubercles still more so. The Carnivora form an inter- 

 mediate group in these characters. 



I must notice however the remarkable exception which the 

 Seals and Cetacea form : they both have a highly organized 

 brain ; the Seals as compared with other Carnivora, and the Ceta- 

 ceans immensely so, as compared with the orders near which they 

 are placed. We should however perhaps take into consideration 

 that the brain has to be educated from without ; and when we 

 perceive the imperfections in the educatory media — the senses — 

 in the Whales, where the organ of smell is either wanting or exists 

 only in a very imperfect condition, where the hands are trans- 

 formed into fins covered by a common integument, we can con- 

 ceive that the highly organized brain is given to the Whale to 

 compensate for these deficiencies, and that its intelligence is not 

 necessarily in degree equal to what might be inferred from the 

 consideration of the brain abstractedly. The same remarks will 

 apply to a certain extent to the Seals, and to some other mammals. 



In the other classes I will not pretend to say that the order 

 of succession of the groups will display the modifications exhi- 

 biting a higher or lower grade of organization in the brain ; the 



* The brain of Midas rufimanus is figured and described by Prof. Owen 

 in Part I. of the Philosophical Transactions for 1837. 



