NERVES OF THE BEAIN. 241 



In conclusion, and in explanation of the marked difference in the origin of 

 the nerves of the spine and of the encephalon, we shall find that it is principaUj^ 

 owing to the columns of motion and sensation. 



1. AU the nerves of Sense, — the olfactory, optic, auditory, not excepting the 

 gustatory, though running into the base of the brain, must deviate from the an- 

 terior column, which is that of motion ; and, accordingly, they twist round that 

 column to enter directly into the sensorium (as the olfactory does), or to associate 

 with the column of sensation, like the optic tractus, and roots of the auditor}'^ 

 nerve. 



2. The next source of irregularity of form and apparent intricacy in the base 

 of the brain, is a consequence of the various sensibilities and active powers of the 

 eye and its appendages, which require no fewer than six nerves to this one organ ! 

 Hence the ophthalmic of the fifth nerve, in addition to the proper optic nerve, — 

 hence the motor independently of the fifth, — hence the sixth and the fom-th, to 

 associate the deep and superficial muscles of the eye and eyelids. 



3. Another som"ce of intricacy is the intrusion, as it were, of the fifth nerve 

 among those of the encephalon. The fifth, a nerve of double root, a sensitive 

 and motor nerve, a nerve with a distinct ganglion on its posterior root, 1 earl}'^ 

 announced to be a spinal nerve, that is, the anterior or (in the human body) the 

 superior of the spinal nerves. This nerve not only giving motion to the jaws, 

 but being the nerve of sensibility, mingles its branches with every other nerve, 

 goes every where in the head and face, and enters into every organ, and is there- 

 fore a source of exceeding great intricacy, untU the just principle be obtained.* 



4. Lastly, a main source of intricacy in the nerves of the base of the brain, and 

 of the whole nervous system, is the existence of a distinct som-ce of motion inde- 

 pendent of volition, and yet necessarily conjoined to it, — a source of power which 

 shall govern the act of respiration, and yet permit a union of the apparatus of 

 breathing with those of speech; for example, the necessity of joining the motion 

 of the features with the pneumatic office of the lungs, being the cause of that 

 deviation which we perceive in the facial nei-ve from those of simple volition. 



In short the double origin and double function of the nerves of the spine is 

 the reason of their uniformity and simphcity of distribution. The nerves of the 

 brain differ from those of the spine, and from each other, inasmuch as each has a 

 peculiar endowment, and necessarily a distinct origin. They therefore vary in 

 course and distribution, and hence then- apparent intricacy. 



* The discovery of this fact has been caught at by men, as incapable of the induction which led to 

 it, as of following it up in its consequences. 



VOL. XIV. PART I. H h 



