294 FUNCTIONS OF THE NERVOUS SYSTEM. 



tion, are those which Sir C. Bell has grouped together in his respiratory 

 system. The most important of these, the Phrenic, arises from the upper 

 part of the Spinal Cord; the Intercostals much lower down; whilst the Facial 

 nerve and the Spinal Accessory, to the latter of which, as will hereafter be 

 stated ( 408), the motor powers of the par vagum are chiefly due, take their 

 origin in the Medulla Oblongata itself. But we must not decide upon the 

 connection of a particular nerve with a particular segment of the Spinal Cord, 

 simply because it diverges from it at that point. It has been shown that, in 

 the Mollusca, a nerve passing to, or proceeding from, one ganglion, frequently 

 passes through or over another which lies in its course ; and in the Articulata, 

 this is a still more constant occurrence. It is by no means improbable, then, 

 that the connection of the intercostal nerves is really in part with the grey 

 matter of the Medulla Oblongata; at any rate, such a connection has not been 

 disproved. The white columns of the Spinal Cord consist of fibres, which 

 bring the spinal nerves into connection, not only with the brain, but also with 

 other segments of the ganglionic portion of the cord ; being analogous in func- 

 tion, not merely to the distinct fibrous tract of the ventral column of the Arti- 

 culata, but also to the fibrous bands that connect the ganglia themselves. And 

 as the Medulla Oblongata, in Vertebrated animals, is the chief centre of the 

 actions of Respiration, it can scarcely be doubted that all the nerves concerned 

 in that function have a direct structural connection with it. 



377. That the Respiratory movements, as ordinarily performed, are essen- 

 tially independent of the Will, appears not only from our own consciousness, 

 but also from cases of paralysis; in some of which, the power of the will over 

 the muscles has been lost, whilst the movements have been kept up by the 

 reflex action of the Medulla Oblongata or respiratory ganglion ; whilst in 

 others, some of the respiratory muscles have been motionless during ordinary 

 breathing, and yet have remained under the power of the will. Such cases 

 are mentioned by Sir C. Bell, in the Appendix to his work on the Nervous 

 System. That consciousness is not a necessary link in the chain of causes, 

 which produce the respiratory movements, we are enabled to judge from the 

 phenomena presented by the human being in sleep and coma, by anencephalous 

 foetuses, and by decapitated animals. Further, Dr. Ley* has put on record a 

 case, which confirms this particular inference, just in the same manner as the 

 cases already related confirm the general doctrine of the non-existence of sen- 

 sibility in the Spinal Cord. He had under his care a patient, in whom the 

 par vagum appeared to be diseased; the lungs suffered in the usual way in 

 consequence, and the patient had evidently laborious breathing; but he dis- 

 tinctly said that he felt no uneasiness in his chest. The experience of every 

 one informs him, that Respiratory movements are partly under the control 

 and direction of the will, though frequently unrestrainable by it. In ordinary 

 circumstances, when the blood is being perfectly aerated, and there is a suffi- 

 cient amount of arterial blood in the system to carry on the functions of life 

 for a short time, we can suspend the respiratory actions during a few seconds 

 without any inconvenience. If, however, we endeavour to prolong the sus- 

 pension, the stimulus conveyed by the excitor nerves to the Medulla Oblon- 

 gata becomes too strong, and we cannot avoid making inspiratory efforts ; and 

 if the suspension be still further prolonged, the whole body becomes agitated 

 by movements, which are almost of a convulsive nature ; and no effort of the 

 will can then prevent the ingress of air.t It is easy to understand why, in 



* On Laryngismus Stridulus, p. 417. 



t It is asserted by M. Bourdon (Recherches sur le MeVanisme de la Respiration, p. 81), 

 that no person ever committed suicide, though many havo attempted to do so, by simply 

 holding the breath; the control of the will over the respiratory muscles not being suHieiently 

 great, to antagonize the stimulus of the " besoin de respirer," when this has become aggru- 



