254 MORPHOLOGY OF THE CEREBRAL CONVOLUTIONS. 



same communication he notices the constancy manifested in the convoluions and 

 speaks strongly in favor of the conclusion that the Assuring of the hemispheres in 

 the course of development follows a determinate plan or law. In his Comparative 

 Anatomy of Vertebrates, Vol. III., he distinguishes three leading patterns of con- 

 voluted surfaces, which, from the prevalent direction of Assuring, he terms the 

 oblique, longitudinal and transverse, and these are exemplified respectively in the 

 ungulate, unguiculate and quadrumanous division of his sub-class Gyrencephala, 



Leuret 1 has shown by an extensive study of the convolutions in the various 

 divisions of the mammalia that certain convolutions are constant, and that in allied 

 genera the character of the cerebral surface is the same. He finds that the convo- 

 lutions are similar in the same animal, and he attempts to classify the mammalia 

 by means of the arrangement of their convolutions. He distinguishes an internal 

 convolution on the mesial surface of the brain and a varying number of external 

 convolutions lying on the lateral aspect, which he names. He classifies animals 

 according to their convolutional characters into fourteen groups. 



In the first group are contained animals taken from various families. The 

 convolutions are absent, the fissures of Sylvius being alone present. In this 

 group he places animals derived from the Cheiroptera, Insectivora, Marsupialia, Mon- 

 otremata and largely the Rodentia. 



In the second group the convolutions are still absent, but there are depressions 

 which announce as it were their approach. It contains Rodents, Insectivora and 

 Marsupials. The fissure of Sylvius now becomes well marked. 



The third group contains the fox, wolf, dog, etc. 



The fourth, animals of the genera of cats and hyena. 



The fifth, the civet, coati, ferret, weasel, otter, etc. 



The sixth, only the ichneumons. 



The seventh, the sloth, African ant-eater, Phosacolonys ''and Hyrax. 



The eighth, kangaroo, Orycteropus and Pteropus. 



The ninth, the Ruminants and other herbivora. 



The tenth, the hog, peccary, etc. 



The eleventh, seal. 



The twelfth, dolphin, porpoise and whale. 



The thirteenth, the elephant. 



The fourteenth, the lemurs, monkeys and apes, thus placing Man in a division 

 alone. 



The number, form, arrangement and relations of the cerebral convolutions 

 says Leuret " are not formed at hazard, every family of animals has a brain con- 

 structed in a determinate manner, and the differences of opinion on the subject 

 arise from a want of attentive examination of a sufficient number of brains. Ob- 

 servation has thus shown what strict induction would lead us to conclude. How, 

 indeed, can we believe that the most important organ of the economy, that by 



1 Anatome compar£e du Systfeme nerveux consid6re dans ses rapports avec l'intelligeuce. Paris, 1839-57. 



