NERVOUS FUNCTIONS. 609 



In regard to the double function of the nerves, 

 it was long ago taught by Herophilus and Era- 

 sistratus, that some are designed for sensation 

 alone, and others for the purpose of regulating 

 the voluntary movements of the body. This 

 theory has been recently submitted to the test 

 of experiment by the late Sir Charles Bell, 

 Magendie, Mayo, Muller, and other physiologists, 

 who although they differ on some points, main- 

 tain that the nerves arising from the posterior 

 portions of the spinal marrow, including the optic 

 and olfactory nerves, branches of the 5th, 7th, 

 8th, and 9th pairs, are destined for sensation ; 

 while those arising from the anterior portions of 

 the spinal marrow, like the 3rd, 4th, 6th, and 

 branches of the 5th, 7th, 8th, and 9th, are regarded 

 as voluntary or motory, and wholly destitute of 

 sensibility. 



But as yet, the discrepancy between the results 

 of different experimenters, and even of the same 

 individuals, leave it more than doubtful whether 

 there be any such thing as insensible nerves. 

 For Magendie has arrived at the conclusion from 

 more recent experiments, that " the roots of the 

 sensitive and motor spinal nerves are equally sen- 

 sible when they are both entire. But if the sensi- 

 tive nerves be cut, the motor immediately lose 

 their sensibility. And if the motor nerves be cut 

 across at the middle of their roots, the end which 

 remains attached to the spinal cord is perfectly 



