THEIR LIFE AND AFFINITY. 249 
strongly, towards that insertion of the nerves, according as the action 
of the nerves is increased or diminished by its centricity ; and it is 
thus that they determine the muscular contraction, and all animal 
motion. The following figure will explain the contraction and relaxa- 
tion of the muscle: a 6 represents the relaxed muscle, and ¢ the nerve 
in its usual state; de the contracted muscle, and c2 the nerve in in- 
creased action. In the second figure, the contraction of the muscle by 
means of a diminution of volume is explained by the closer approxi- 
mation of the points to the centre. 
Fie Whine ce Cll Seibrioyicievep SP A Ses silecg ds ice 
But besides this twofold termination, the nervous system finally branches 
out also into the vegetative sphere of the body, thus partly determining 
both sensation and motion, and partly constituting the bond of unity 
between the different organs of the vegetative system. In the latter 
point of view the very form of the nervous fibres is remarkable, since 
they all have an evident tendency to inclose the intestines and vessels 
in a kind of network. In the same point of view it becomes clear also 
that, as the inclosing of the lower system in the higher one is charac- 
teristic of animal organization, and the rudiments of the nerves always 
show this peripherous type, the higher animals, and man in particular,— 
in whom the spinal nerves encompass the common cavity of the trunk, 
somewhat similarly to the bending of the ribs,—possess a system of 
nerves appropriated to the vegetative structure, and perfectly analogous 
to the nervous system of the inferior animals, namely, the ganglionic 
system, or that of the great sympathetic nerve. 
The osseous system is developed uniformly with that of the nerves, 
and issues out of the vertebral column, as the nervous system does out 
of the spinal marrow; whilst the vertebral column forms at first but an 
isolating sheath around the latter, as an earthly substance most power- 
fully attracted by the nervous system, acting like the sun, and for 
the most part antagonistically upon the other parts of the body. In 
a somewhat similar manner, among falling bodies of different specific 
gravities, the heaviest will always lie undermost and nearest to the at- 
tracting centre of the earth. Where the osseous system has acquired 
its most perfect structure (in the skull) it presents also the original 
type, the spherical form ; on the contrary, like the radii of the nervous 
system, it branches out more and more in the extremities, a fact which 
is clearly seen in the increasing number of the bones in each member, 
from their root in the trunk to the ramification in the fingers and 
toes. 
