548 ANIMAL PHYSIOLOGY. 
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 oth- . 
ers employed in the final elaboration of sensory ones. 
It is even yet premature to dogmatize in regard to the site 
of these centers; especially are we not ready for large generali- 
zations. In man the convolutions around the fissure of Rolando 
constitute the motor area best determined, 
The whole subject of cortical localization requires much ad- 
ditional study, especially by the comparative method in the 
widest sense—i. e., by a comparison of the results of operative 
procedure in a variety of groups of animals, and the results of 
clinical, pathological, physiological, and psychological investi- 
gation. Especially must allowance be made for differences to 
be observed, both for the group and the individual; and also 
for the influence which one region exerts over another. Be- 
tween the weight of the cerebrum, the extent of its cortical 
surface, and psychic power, there is a general relationship. 
GENERAL REMARKS ON THE SENSES. 
Our studies in embryology have taught us that all the vari- 
ous forms of end-organs are developed from the epiblast, and 
Fig. 398.—Papillee of skin of palm of hand (after Sappey). A vascular network in all cases, 
and in some nerves and tactile corpuscles, enter the papille. 
