.578 MU. YouATr’s veterinary lectures. 
What takes place when the crura cerebri pass under the crura 
cercbelli, according to the simile of Varolius, like a river under a 
bridge ? Anatomists have talked of the transverse fibres of the 
cerebellum, and the longitudinal ones of the cerebrum, and of 
the latter being traced low dowm through the loci nigri, even to 
the corpora striata; but, w hether because the pons varolii is smaller 
in our patients, or I have not used sufficient diligence, I confess 
that I have found only faint and uncertain traces of these things ; 
but I have found, and this vertical section of the pons will suffi¬ 
ciently exhibit it, the base of the arch of the bridge composed 
almost entirely of the medullary matter of the cerebellum; that 
as it ascends the side of the arch, it is gradually mingled with 
and lost in the darker-coloured matter of the crura cerebri, until, 
when I arrive at the crown of the arch, there is only a thin pel¬ 
licle of medullary matter remaining. Then, at the crown of the 
arch, I have observed two medullary longitudinal bands or tracks 
of white substance, evidently the continuation of the corpora py- 
ramidalia of the medulla oblongata, and of the central columns 
of the inferior surface of the spinal chord. I have cut trans¬ 
versely and vertically across the crura cerebri, a little posteriorly 
to the origins of the third pair of nerves, and the band or track 
was still visible. I have made a similar section a little more an¬ 
teriorly, and beyond the origins of these nerves, and all trace of 
it had vanished. I have returned to the pons varolii, and I have 
observed a central medullary band occupying the sulcus on the 
crown of the arch—an evident commissure—an evident union of 
the medullary matter of the two pedicles of the cerebellum ; and, 
looking attentively below this, I have traced a line of separation 
between the two sides of the bridge, or rather between the crura 
cerebri which run under the bridge, and I have begun to perceive 
the central columns of the superior surface. I can fairly make 
out the rudiments of four of the columns of which I shall pre¬ 
sently find the spinal chord to be composed, and somenotionsof the 
structure and functions of this part of the brain begin to present 
themselves, to which however I must not yield too hasty belief. 
I attach importance, however, to the gradual mingling of the 
matter of the cerebellum with that of the cerebrum, and this 
mingling of substance taking place in the direction of the inferior 
surface of the brain, and also the prolongation of the medullary. 
I must not yet call it the motor track along the centre of the same 
surface. 
The MedullaOblongata .—This portion of the brain, of amingled 
oblong and quadrilateral figure, I know to be most important, for 
it will not bear the slightest injury ; pressure upon it causes im¬ 
mediate stupor, and if it is cut asunder, consciousness is in a 
