182 
ANIMAL PATHOLOGY. 
of many a disease of the motor system. I shall shortly return 
to this point, but, in the mean time, we must proceed to the 
superior (posterior) surface of the cord, and cast a rapid glance 
at its physiology and diseases. 
The superior {posterior) Surface of the Cord. — A very different 
structure here presents itself. This surface of the cord is flatter, 
lower than the other. We have not the deep central sulcus, 
nor the rounded columns, nor the connecting fibres. We look 
more closely, and we find that the cord is composed of four 
columns. There was a line superficial, faint, and not always to 
be traced, running along each of the columns of the inferior 
surface, towards the lateral portion of it; but here are sulci, 
and of considerable depth, and plainly dividing the upper face* 
of the cord into four partitions of nearly equal breadth. The 
preparation which I now hold in my hand of the cervical portion 
of the spinal cord of a horse, well illustrates this. Here are 
four distinct columns — the central ones devoted to sensation, 
for in the sulcus between them and the lateral ones, and evi- 
dently springing from the central columns, are the roots of the 
sensitive nerves. With the functions of the lateral columns 
I have at present nothing to do. 
The sensitive Columns and Nerves. — In former lectures it was 
clearly shewn that this portion of the superior aspect of the cord 
might be traced up to that division or part of the brain which gives 
origin to nerves of pure sensation. The fibres of these columns 
pursue their course longitudinally down the cord ; each column 
perfectly distinct from, and unconnected with, the other. At 
certain distances, corresponding with the foramina of the spine, 
some fibrils or threads are detached from the column ; they ap- 
proximate, they unite, they run into and form a ganglion ; and 
the nerve thus formed, pursuing its course, when it arrives at and 
is penetrating the dura mater, meets with a fasciculus of fibres 
from the inferior surface : and they coalesce ; and there is formed 
around them a common sheath ; and they still proceed to their 
destination, apparently a single nerve, but possessing a double 
function — that of communicating to the common sensorium 
impressions from without, and exciting muscular action. 
I will not repeat the substance of former lectures as to the 
proof of the different functions discharged by these nerves, but 
I will assume that their ramifications do extend over the whole 
surface of the body ; and that they form a kind of net-work or 
tunic upon it : that while they accumulate on certain parts and 
communicate proportionate sensibility, there is no part of the 
animal that is not, to a greater or less degree, made susceptible 
of certain impressions, pleasurable or painful. “A change is 
