1815.) = Intellectual Functions of Man and Animals. 121 
succeeded Willis conjectured that there were cerebral and cere- 
bellic nerves, ‘They indeed only conjectured this ; and they, more- 
over, erred by distinguishing them into vital and animal. ‘The viral 
nerves, said they, are chiefly derived from the cerebellum, and the 
animal from the cerebrum.—They have lelieved, says Haller, that 
several nerves have roots partly from the cerebellum. But Haller 
objects that the fifth pair arising, as he says, trom the cerebellum, 
is appropriated both to sense and to motion ; “ nor would,” says he, 
«© Nature have so solicitously blended both species of nervous fibres 
if their nature had been different,” and if, he might have added, 
they had been destined to supply totally distinct parts of the body. 
He shows also, that some of those nerves which they believe to 
have some origin from the cerebellum, have nothing to do with 
vitality ; and he adduces various other objections. Speaking of the 
possibility of fibrils of different kinds being in the same nerve, 
Haller also says, ‘* Infinitum ad infinitessimum possis deponere, 
falli hominem, qui Dei consilia voluerit conjectura expiscari.” 
Even Haller, however, when speaking of the double series of roots 
of the: spinal nerves, involuntarily allows some connection of that 
kind; for he says, “* quarum anterior altefa in eodem cum cerebral- 
ibus nervis ordine pergit, posterior medulle propria est, et demum 
sub fine quarti ventriculi incipit. | 
In proof, however, that the sensitive and motive nerves are per- 
fectly distinct, I can quote for Dr. Leach a much better authority 
than that of any old author: first, that of reason, which tells us, 
that as sensation cannot reach the cerebrum without an ascending 
» motion—a motion towards the brain; as the consequent volition 
cannot affect the muscles without a descending motion—a motion 
from the brain ; and as it is contrary to all analogy that there should 
be motion in opposite directions in the same tubes of neurilema— 
for these reasons, there must be a series of nerves appropriated to 
each: and, secondly, the authority of anatomy, which shows us 
that, though nerves supplying parts which are contiguous in position 
but different in nature often run in one common sheath, yet on 
arriving at the spinal marrow they split into two roots, as they are 
termed ; that these roots are quite different in form, the anterior 
being more fibrous, and the posterior more simple and round ; that 
the anterior roots join the anterior columns of the spinal marrow, 
and the posterior roots the posterior columns; that these columns 
actually do join the cerebrum and cerebellum respectively ; and that 
even those cerebral nerves which are at once nerves of sensation and 
volition have two roots, one from the cerebrum, and another from 
the cerebellum. This may be most easily observed in the seventh 
pair or facial nerves, the origin of which has hitherto been mis- 
taken by all anatomists. They directly penetrate the medulla 
oblongata from its lower to its upper surface ; and, throughout this 
very considerable internal passage, each nerve consists of two per- 
fectly distinct, silvery and glistening cords, of which one joins the 
pactallurs, and the other rans onward to the cerebrum, ‘This may 
i) 
