1885.] The Relations of Mind and Matter. 689 
retains the dim vagueness which probably exists in animals of a 
very low grade. But in the cerebro-spinal system consciousness 
has become sharply centralized and defined. The peculiar condi- 
tion which we call consciousness may have its roots very low 
down in the soil of nature as a highly generalized accompaniment 
of motor energy. In.the evolution of higher forms and condi- 
tions it has grown steadily more specialized, until, in the central 
nerve organ of man, it has become a concentrated, developed and 
sharply defined condition, the necessary accompaniment of an 
equally special centralization of substance and energy, which we 
name the mind. 
The cerebro-spinal nerve system in man and the higher ani- 
mals has become a highly differentiated and complex organism, 
whose make-up may be very briefly described. The sensory 
nerves, which convey motor impressions from the various points 
of the surface, pass through a series of spinal ganglia in their 
upward journey toward the brain. .Here they enter the great 
ganglia at the base of the brain, to which the nerves of some of 
the special senses pass directly. From here they communicate 
with the cerebrum, though whether directly or indirectly is not 
certain. It is certain that when the cerebrum is removed many 
of the sensory nerves are found to be in direct communication 
with those of motion. It is almost equally certain that in ordi- 
nary cases many sensory impressions are directly passed on to 
the motor nerves, with or without consciousness. These inter- 
mediate ganglia, then, may perform a special duty in the economy 
which we will consider further on. From the cerebrum motor 
nerves enter these ganglia, from which the same or other motor 
nerves emerge and pass onward, mainly by the route of the spinal 
. ganglia, to the muscles. 
According to M. Luys! the cerebral organ is composed of a 
vast array of fibers which diverge to enter a hemispherical sheet 
of gray or cellular nerve matter. This gray sheet is greatly 
wrinkled and folded so as considerably to increase its superficial 
extent. It is of no great thickness, and is composed of succes- 
sive layers of nerve cells connected by fibers, these cells being 
smaller in the surface layers and growing larger in the deeper 
layers. The hemisphere is really a double mass, since it is 
divided in the middle line of the body, the two halves being con- 
1 The Brain and its Functions, International Scientific Series. 
