THE EXTINCT MAMMALIA. 307 



times Yery effective in mechanism. In many primary ungulates, 

 the primitive condition of four conical tubercles is found. In 

 passing to older periods we find the Mammalia of the Puerco 

 period, which never have more than three principal tubercles, 

 with the exception of three or four species. In the succeeding 

 periods, however, they get the fourth tubercle on the posterior 

 side. Finally, you get a complicated series of grinding or cutting 

 apparatus, as the case may be. 



Last, but not least, we take the series of the brain. No doubt 

 the generalization is true, that the primitive forms of Mammalia 

 had small brains with smooth hemispheres ; later ones had larger 

 brains with comj^lex hemispheres. In general the Carnivora have 

 retained a more simple form of brain, while herbivorous animals 

 have retained a more complicated type of brain. The lowest 

 forms of Mammalia display the additional peculiarity of having the 

 middle brain exposed ; and the hemispheres or large lobes of the 

 brain, which are supposed to be the seat of the mental phenomena, 

 are so reduced in size at the back end, that you see the middle 

 brain distinctly, though it is smaller than in reptiles and fishes. 

 (See Plate XIV.) 



It is beyond the possibility of controversy, that these series 

 have existed, that they have originated in simplicity and have re- 

 sulted in complication ; and the further induction must be drawn, 

 that the j^rocess of succession has been toward greater effective- 

 ness of mechanical work. There are also cases of degradation, as 

 in the growing deficiency in dentition in man. There is no doubt 

 that a large number of people are now losing their wisdom-teeth 

 in both jaws. 



We are now brought to the question of the relations which 

 mind bears to these principles. The question as to the nature of 

 mind is not so complex as it might seem. There is a great deal 

 of it, to be sure ; but on examination it resolves itself into a few 

 ultimate forms. An analysis reduces it to a few principal types or 

 departments — tlie departments of the intelligence and of the emo- 

 tions (with their primary simj^ler forms, likes and dislikes), and 

 the will, if such there be. These three groups, proposed by Kant, 

 are well known, and arc adopted by many metaphysicians ; and 

 they stand the scrutiny of modern science as applied to botii men 

 and the lower animals. But the question of the material of the 

 mind, the original raw stuff out of which mind was made, is one 

 which is claiming attention now from biologists, as it always has 



