SIR CHARLES BELL ON THE NERVOUS SYSTEM. 
253 
may be permitted to doubt, if in common breathing- there is any sensation ; we are 
certainly not conscious of it. It cannot at least be anything- like the exercise of sen- 
sibility of which we are conscious, and which is wearied and exhausted by repetition. 
There is then, we must apprehend, another source of the regulated drawing of breath, 
which excites the respiratory muscles not to occasional and sudden actions, but to 
the constant combined action of opening the passages to the air. Even in the de- 
capitated head, this influence will cause the muscles of the nostrils to be drawn re- 
peatedly, as in natural breathing*. 
Of the Supply of Blood to the Nerves of the Respiratory System. 
We have seen that the lateral part of the medulla oblongata and cervical part of 
the spinal marrow are more necessary to life than the brain itself ; that as on this 
part and the nerves thence arising, the actions of respiration depend, the phenomena 
of life depend more directly upon them than on any part of the animal body. 
It being at the same time perfectly well understood, that no quality of brain or 
nerve, or vital property in any part, can exist without a supply of arterial blood, it be- 
comes an object of interest to know how nature has provided for a bountiful arterial 
circulation to these important organs. 
Our books, in treating of the circulation in the brain, state that the supply of 
blood to it is very much greater than to any other part of equal weight. This is cor- 
rect, and would of itself mark the importance of the organ. But in proceeding to 
show how this is accomplished, they state, that four great arteries ascend to the 
brain, and that of these the vertebral arteries, for greater security against the supply 
of blood being dangerously diminished, ascend through the foramina in the cervical 
vertebrae. We object to this last conclusion. 
It is not to secure the free circulation through the brain that the vertebral arteries 
take this tortuous and concealed course. It is for the supply of arterial blood to 
these vital nerves, and to that part of the spinal marrow which gives origin to them. 
This idea suggested itself to me on observing, in a subject minutely injected, with 
what a copious supply of tortuous arteries these nerves and the side of the medulla 
oblongata were surrounded. When these arteries, branches of the vertebral artery, 
and their accompanying veins were removed, we saw the foramina by which they 
enter into the respiratory column conspicuous beyond what is seen in other parts. 
This opinion was pointed out in a former paper-f- ; but the subject acquires a higher 
interest from the observations of Sir Astley Cooper. Fie found that, on compress- 
ing the vertebral arteries at the lower part of the neck, where they are about to enter 
* The head gasps in successive actions after decapitation. — Legallois. Breathing continued after the 
pithing of the animal in the cervical region, and after the brain and cerebellum had been removed and the vagi 
divided in the neck. — Dr. Reid. “ I have seen the respiratory muscles twice called into simultaneous movement 
after all the thoracic viscera had been rapidly removed,” &c. — Dr. Reid. 
t See the Nervous System, p. 119. 
