122 Sketch of a General Theory of the [Aue. 
easily be seen by any anatomist who chooses to look at the subject 
itself, instead of only making such a “ careful examination ” as 
Dr. Leach last instituted on “ the spinal mass of nerves.’ 
The views which I have now taken enable me to answer a most 
important question on this subject, which has twice been put by 
Soemmerring. After stating the opinion that the use of the ganglia 
is to place certain parts out of the power of the will, or to change 
yoluntary into spontaneous motions, he asks why the spinal ganglia 
are formed only on the posterior roots—‘‘ Qua causa est,” says he, 
“ cur in radice posteriore tantum nervorum spinalium ganglia inve- 
niuntur, minime autem in priore?” And again, “ Cur radix prior 
nervorum sping medulle, adeo vicina, ganglia non immiscitur?” 
The obvious answer to these two questions is, that the anterior 
roots, as stated above, have nothing to do with motion—are those 
of sensation alone; while the posterior, being those of motion, it 
is on them alone that ganglia can be necessary to impede the im- 
pulse of the will, or to change, in some of their fibrils, voluntary 
into involuntary motion. 
Now as in this situation, ganglia impede voluntary motion, so in 
others do they impede sensation, and prevent the brain being dis- 
turbed by all the impressions on the viscera, which would have been 
incompatible with thought. Such, then, are the ganglia of the 
viscera, &c, ; for wherever the anterior spinal branch communicates 
with the great sympathetic, there is a ganglion at the place of this 
union. Thus there are ganglia of sensation as well as ganglia of 
motion; and these ganglia are always as near as possible to the 
origins of their respective nerves :—in other words, as these sensitive 
or ascending nerves originate from the internal surfaces of the body, 
their ganglia, which prevent sensation reaching the sensorium com- 
mune and becoming perception, are placed nearer to their system— 
the great sympathetic nerve, and the organs from which they arise; 
and as the motive or descending nerves originate from the cere- 
bellum, their ganglia, which prevent volition reaching certain 
muscular parts, are placed nearer to their system — the cere- 
bellum, &c. That the ganglia are admirably adapted thus to 
impede sensation, as I have stated, and volition as conjectured by 
Johnstone, and confirmed by these remarks, is evident from the 
observation of Cuvier, that the ganglia of red-blooded animals do 
not differ much from nervous plexus; that even the simple ganglia, — 
or those formed by a single nerve, are resolved by maceration into 
several filaments which anastomoze together ; and that in the crus- 
tacea, insects, and worms, the ganglia are mere homogeneous en- 
largements of the medullary cord to which they belong. All of 
these circumstances are well adapted to impede the motion which 
takes place in them—a motion, however, which is only of this 
kind, that each globule communicates its impulse to a succeeding 
one; and, as the last of a series of globules must thus move the 
instant that the first is impelled, the extreme velocity of nervous 
action is thusconceivable. It does not follow, however, that all the | 
