544 ANIMAL PHYSIOLOGY. 
certain parts, crowding and alteration of shape, owing to the 
influence of its bony case, its membranes, etc. 
Fic. 394.—A, brain of aye-aye (Lemur); B, of marmoset ; C, of ec uiree morkey (Callithrix); 
D, of macaque monkey; E, of gibbon; F, of a fifth-month human feetus (after Owen). 
Although naturalists are agreed that the monkeys, apes, and lemurs are related, consider- 
able differences are to be observed in their brains. ese figures also illustrate the remark 
made after the following ones. 
It is evident, from an inspection of the cranial cavities of 
those enormous fossil forms that preceded the higher verte- 
brates, that their brains, in proportion to their bodies, were 
very small, so that any variation in thé direction of increase 
in the encephalon—especially the cerebrum—must have given 
the creatures, the subject of such variation, a decided advan- 
tage in the struggle for existence, and one which may partly 
account, perhaps, for the extinction of those animals of vast 
proportions but limited intelligence. That the size of the brain 
Fia. 395.—A, brain of. a chelonian ; B, of a foetal calf; OC, of a cat. (All after Geary) 
T indicates cerebral hemispheres; IJ, thalamus; IZJ/, corpora quadrigemina; IV, cerebel- 
lum; V, medulla; st, corpus striatum ; f fornix ; h, hippocampus ; sr, fourth ventricle ; 
, geniculate body ; ol, olfactory lobe. It will be observed (1) how the foetal brain in a 
Biches animal form resembles the developed brain in 4 lower form, and (2) how certain 
_parts become crowded together and covered over by more prominent regions, e.g. 
«cerebrum, as we ascend the animal scale. 7 oe 
