190 
ANIMAL ACTIVITIES. 
every muscle for that purpose is the nervous system. 
This consists of a brain connected with the spinal cord, 
and a series of ganglia with nerve connections - in the 
visceral cavity. From these centres nerves run to all 
parts of the body. The division between brain and spinal 
cord is not so sharp as in man. The brain itself has the 
same parts as the brain of man, but these parts do not 
have the same shape or relative size (Figs. 15 3 and 154). 
Fig. 148.—The Use of a Muscle. 
Notice how large the olfactory and optic lobes appear 
in the frog. In man they are small and do not show 
in the figure. In man, too, the cerebrum or forebrain 
has grown so large that it occupies almost the whole 
of the brain-cavity. These facts of structure would 
seem to indicate that sight and smell are of more im¬ 
portance to the frog than memory or reason. 
Discovery. It is the duty of the nervous system to 
keep in touch with the outer world, in order that the 
movements made may be useful to the animal. 
