1851.) OF THE ROYAL INSTITUTION. 39 
scapular muscles, we find that each of these sections is connected by 
four distinct roots with the common myelonic centre. 
In man five segments enter into the formation of the en- 
largement from which the nerves of the brachial plexus are 
derived, and the different sets above enumerated may be shown to 
have connexions for the most part with the whole of them, or at 
least with four out of five. For instance, the nerve which supplies 
the muscles for extending the arm and the fingers (radio-spiral), if 
traced to the myelon, will be found to divide into five roots, and the 
same may be said of the nerves belonging to the other sets. These 
facts can scarcely admit of any other explanation than that here 
given, namely, myelonic origin. 
The independent mechanism of this system was illustrated by 
reference to the ordinary functions of breathing, swallowing, the 
motions of decapitated animals, and some morbid states. 
The supposed existence of two systems in the body for motion, — 
one mechanical, having its roots in the myelon, and the other voli- 
tional, having its roots in the brain, — was considered inadmissible. 
There is probably but one system, namely the myelonic, which is 
subordinated in different degrees to the encephalon (brain), according 
to the purposes it is intended to subserve. Those parts of it which are 
in communication with the nerves supplying the extremities, are com- 
pletely subordinated. Others, as for instance those which give 
origin to the nerves of respiration and deglutition, only partially so; 
by this subordination, animals have the power of producing their 
various volitional movements through the instrumentality of a system 
whose power is in itself, but under the restraint and direction of the 
will. 
On considering the steps of the process by which we use this 
mechanism, it will be readily admitted, that subjectively, we have little 
orno influence. Thus, however well we may be acquainted with the 
structure and position of the muscles and nerves of our arms, we 
cannot excite directly any one of them we may desireto select. Such 
power, if we possessed it, would be altogether useless, inasmuch as by 
far the largest number of men, and all animals, must ever remain 
ignorant of their own structure. On the other hand an objective 
intention instantly calls forth the means necessary to produce the 
desired result. As by the principles of common sense (using this ex- 
pression as Reid used it) we refer sensations to the objects producing 
them, so in the use of our muscular machine we have no other guide 
or power than this objective one, which our proper constitution sup- 
lies. 
: The relation of external impressions to resultant movements is 
therefore of particular interest. It has been already stated, that some 
animal movements are merely physical (auto-myelonic) excited by 
external impressions and unattended by any consciousness. Next to 
these and in close alliance with them are movements also following 
directly from an external impression, which although it be felt, still 
