514 COMPARATIVE PHYSIOLOGY. 



of "the brain." We are conversant with certain phenomena 

 referable to this organ in a number of animals, cliiefly the 

 higher mammals ; but our knowledge is as yet insufficient to 

 generalize, except in the broadest way, regarding the functions 

 of the brain — i.e., to determine what is common to the brains of 

 all vertebrates and what is peculiar to each group. Referring, 

 then, to the higher mammals, especially to the dog, the cat, the 

 monkey, and man, we niay make the following statements : 



The medulla oblongata is functionally the ruler of vegeta- 

 tive life— the lower functions ; and so may be regarded as the 

 seat of a great number of '' centers," or collections of cells with 

 functions to a large degree distinct, but like close neighbors, 

 with a mutual dependence. 



Phylogenetically (ancestrally) the medulla is a very ancient 

 region, hence the explanation apparently of so many of its 

 functions being common to the whole vertebrate group. 



Parts of the mesencephalon, the pons Varolii, the optic lobes 

 or corpora quadrigemina, the crura cerebri, etc., are not only 

 connecting paths between the cord and cerebrum, but seem to 

 preside over the co-ordination of muscular movements, and to 

 take some share in the elaboratioa of visual and perhaps other 

 sensory impulses. 



The cerebellum may have many functions unknown to us. 

 Its connections with other parts of the nerve-centers are numer- 

 ous, though their significance is in great part unknown. Both 

 pathological and physiological investigation point to its having 

 a large share in muscular co-ordination. 



It is certain that the cerebrum is the part of the brain essen- 

 tial for all the higher psychic manifestations in the most ad- 

 vanced mammals and in man. 



The preponderating development of man's cerebrum ex- 

 plains at once his domination in the animal world, his power 

 over the inanimate forces of Nature, and his peculiar infirmities, 

 tendencies to a certain class of diseases, etc., — in a word, man is 

 man, largely by virtue of the size and peculiarities of this part 

 of his brain. \ 



Modern research has made it clear also that there is a '' pro- 

 jection " of sensory and motor phenomena in the cerebral cor- 

 tex ; in other words, that there are sensory and motor centers 

 in the sense that in the cortex there are certain cells which have 

 an important share in the initiation of motor impulses, and 

 others employed in the final elaboration of sensory ones. 



