374 FUNCTIONS OF SPINAL CORD :—REFLEX ACTION. 
- 463. We shall now consider, in more detail, the functions 
of the different parts of the Cerebro-Spinal System in Man 
and the higher animals; referring occasionally to the Inyer- 
tebrated classes for illustrations which they can best afford. — 
We shall commence by examining the functions of the Spinal — 
Cord and Medulla Oblongata, which are the parts concerned — 
in reflex action. 
Functions of the Spinal Cord.—Reflex Action. | 
464. The Spinal Cord of Vertebrated Animals may be con- — 
sidered as a collection of ganglia, analogous to those of which — 
the ganglionic cord of Articulata is composed ; these ganglia — 
being united, however, in an unbroken line, instead of being — 
distinct from one another and brought into communication by 
connecting cords. There is great difficulty in tracing-out the 
precise course of the nerve-fibres which form the white strands — 
of the Spinal Cord ; and it is doubtful how far any of them — 
form a continuous connexion between the roots of the Spinal 
Nerves and the Brain. But there can be no doubt that such ~ 
a connexion is established, either by the fibrous tracts or by ~ 
the grey matter of the Spinal Cord; experiment haying © 
unequivocally shown that the latter participates with the © 
former in this conducting power. r 
465. When the Cerebro-Spinal system is in full activity, — 
its nerves convey impressions from every part of the body to 
the Brain, where they are communicated to the mind,—that is, 
the individual becomes conscious of them, or feels them as 
sensations. And by the fibres of the same system which pass — 
in the contrary direction, the will acts upon the muscles so as 
-to produce voluntary motion. Now the brain is not in com — 
stant action, even in a healthy person ; it requires rest; 2 
during profound sleep it is in a state of complete torpor. Yet 
we still see those movements continuing, which are essential 
to the maintenance of life; the breathing goes on uninter 
ruptedly, liquid poured into the mouth is swallowed, and the 
position is changed when the body would be injured by § 
remaining in it. The same is the case in apoplexy, in which 
the actions of the brain are suspended by pressure oe 
And the same will take place, also, in an animal from which § 
the cerebrum has been removed ; or in which its functi 7 | 
are completely suspended by a severe blow on the head. 
