68 
MR. YOUATT'S VETERINARY LECTURES. 
of that surface ; we have observed, that they seem to be prolon¬ 
gations of the substance of the brain, or to spring bodily from 
that organ, and that through the whole of their course they have 
no anastomosis. To the two first of these peculiarities I shall 
hereafter recall your recollection, when I have to speak of 
the relative situation of nerves of certain functions. The prolon¬ 
gation of the substance of the brain—the long root that can be 
traced deep into the brain—seems natural enough, when we con¬ 
sider that from these three nerves the animal derives almost all 
his knowledge of surrounding objects—all the materials for 
thought and improvement. It seems reasonable that these im¬ 
pressions should be conveyed securely and deeply, there to be 
preserved, arranged, and compared. They are as much identi¬ 
fied with the mind and with animal life, as the well-protected 
organs of the thorax are with the inferior organic principle; and 
the wisdom and benevolence of the arrangement by which these 
impressions of smell, and hearing, and sight, are preserved dis¬ 
tinct and pure, and by which no anastomosis with other nerves 
is permitted, needs no illustration of mine. But I proceed to 
other nerves, differently situated and of different function, viz. 
the nerves of pure motion. 
The Motores Oculi, or Third Pair of Nerves. —About the 
middle of the crura cerebri in the horse (and to this animal, 
if an especial exception is not made, all these anatomical details 
refer), and rather nearer to the corpus albicans than to the pons va- 
rolii, the third pair of nerves take their origin. They seem to 
rise superficially from the crura cerebri ; they cannot be traced 
at all into the substance of the brain, except in a way that I shall 
presently notice, and they are clearly referrible to another surface 
of the spinal chord, or its supposed prolongation—the inferior one. 
Let me here remark, once for all, that from the difference of the 
attitude of the human being and the quadruped, the anterior 
surface of the spinal chord in man, is the inferior one in the 
brute; and the posterior one in the biped, is the superior one in 
the quadruped. These nerves spring from the central column of 
the inferior surface—that track which I have already seen under 
the pons varolii, and along the crura cerebri. They do not, 
however, rise bodily from the crura, but by several minute 
fibriculi ranged in a line , following the course of this medullary 
track. These fibriculi approximate to each other, and unite 
either before they penetrate the dura mater, or as they are leaving 
it, and form a nerve. This is very different from what we have 
observed in either of the nerves of peculiar sensation. 
Course of the Nerve .—The motor oculi takes its course obliquely 
across the crus cerebri, and winds downwards, and enters the 
