NERVOUS SYSTEM. 
69 
cavernous sinuses, and escapes through the foramen .longum 
orhitale into the orbit;—there it divides, and the smaller branch 
goes to the levator oculi, while the larger subdivides, and goes 
to all the other muscles of the eye, except the superior oblique 
and the abductor, for the purpose of moving the eye in its socket. 
Then it is a nerve of voluntary motion . 
Its Anastomoses .—As we follow its course, we observe another 
circumstance in which it differs from either of the sensitive nerves, 
— it connects itself with other nerves It communicates with 
minute branches of the ophthalmic division of the fifth pair, and 
more particularly unites with them to form that curious gan¬ 
glion, the ophthalmic , whence the iris derives its supply of nervous 
influence. I enter not into the cause of this yet. We shall know 
more about it by-and-by, for a thousand anastomoses will come 
before us, the great utility of which will be evident on the 
slightest inspection ; but I content myself with pointing out to 
you how far we are departing from the character of a nerve of 
peculiar sensation. 
The Pathetici , or Fourth Pair of Nerves. —I feel considerable 
difficulty in classing this nerve. It goes to the trachealis or 
superior oblique muscle of the eye, and governs its motion; but 
whether it is a nerve of pure voluntary motion, or merely associa¬ 
ting the motion of the eye with some organic function, and pro¬ 
bably that of respiration, I am not assured. It arises from a 
singular part of the brain,—from the crus cerebri at the base of 
the testes, and, consequently, from the superior surface of the 
prolongation of the spinal chord ; but it does not arise either 
from the centre or the side of the crus—more inclining, how¬ 
ever, to the latter than to the former ;—and when I make a longi¬ 
tudinal incision through the cerebellum, and lay open the whole 
of the fourth ventricle, I plainly see that it does spring from that 
portion of the crus which may be considered as a possible pro¬ 
longation of the lateral column of the medulla oblongata. In 
this respect it differs from the voluntary motor nerve which I 
have just considered, and from every other voluntary motor nerve 
of the brain or the spinal chord. In addition to this, it curiously 
winds its way through the other nerves, and proceeds to this 
single muscle without an anastomosis; nor can I trace to the 
trachealis muscle any fibre from any voluntary motor nerve. 
This is very singular; for with regard to every other muscle 
(the visceral ones excepted), if there are communications from 
an organic nerve to associate the action of that muscle in the 
discharge of some vital function, there are also communications 
from some spinal cerebral nerve for the purpose of voluntary mo¬ 
tion. It arises by filaments, two of which I can plainly trace. 
VOL. VII. K 
