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 ^^ ill explain the contraction and relaxa- 

 tion of the muscle : a b represents the relaxed muscle, and c the nerve 

 in its usual state ; d e the contracted muscle, and c° 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. 



d. 



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 veiy form of the nervous fibres is remarkable, since 

 tliey 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 tj'pe, 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 eartli. 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 

 toea. 



