38 NOTICES OF THE MEETINGS [March 14, 
namely, variety of voluntary movement according to the particular 
requirements of each animal. 
Man, by his adaptation to the erect position, presents the highest 
illustration of this vertebrate intention. His anterior extremities, 
not being employed in locomotion, are left free to become the minis- 
ters of more subtle volitions, to which they are well fitted by the 
unfettered condition of their parts, and by their capability of forming 
an almost infinite variety of combinations. 
On reviewing the extent and kind of movement enjoyed by the dif- 
ferent members of the animal kingdom, it seems probable, that in 
many of the lower forms, the phenomena are of an entirely physical 
nature, and that voluntary power is not manifested until we have a 
corresponding developement of the senses. 
The expression ‘‘ Corpus animale machina muscularis ” is rightly 
applied to that apparatus of bones, muscles, nerves, and myelon* 
which is arranged for our use and subordinated to our will. Nor 
is there anything contradictory to freedom in the admission of a 
pre-arranged mechanism to minister to voluntary action. The law 
of limitation is expressed in the anatomical structure of the parts. 
In the lower animals this is very obvious :— for instance, although 
the bird has the power of employing its wing at will, yet in the wing 
itself there is limitation to certain kinds of movement, namely, to 
folding or extending it, but there is no freedom for other motions. 
What is true of the coarser parts seems to apply to the more delicate 
arrangements in the nervous structure, although they are too 
delicate for our present means of unravelling and displaying them, 
and we are left to read their anatomy by the physiological phenomena 
they present. 
The characters of the myelon which entitle it to be considered 
an independent element of the nervous system were brought under 
notice. Its developement at different parts bears a proportion to the 
corresponding segments of the skeleton. In illustration, its uniform 
size in the viper, and the cervical and lumbar enlargements in the bird, 
as also the mode in which the nerves are connected with it, weredemon- 
strated. The anatomy ofa plexus seems to give us a striking proof of 
myelonic origin of nerves, as opposed to the theory which ‘admits of 
their direct continuity upwards through the myelon to the brain. 
When the motions of the segments of the skeleton are simple, as occurs 
throughout the whole length of the body in the viper, and in the 
cervical and dorsal regions in the bird, the ‘nerves arise by single 
roots ; but where the nervous supply is to parts complicated in their 
structure and adapted for varied movements, the nerves arise by 
many roots. Thus if we divide the nerves of the brachial plexus of 
the bird into four sets, one for folding the wing, one for unfolding 
it, one to go to the strong muscles of the shoulder, and one to the 
* This term is used as first proposed by Professor Owen, to designate the 
series of nervous centres commonly called Spinal Chord. 
