INFLUENCE OF NERVOUS SYSTEM. 227 



Almost all the muscles of the body, in violent efforts of 

 dyspnoea, coughing, and the like, may be brought into 

 action at once, or in quick succession ; but more particu- 

 larly the muscles of the larynx, face, scapula, spine, and 

 abdomen co-operate in these efforts with the muscles of the 

 chest. These, therefore, are often classed as secondary 

 muscles of respiration ; and the nerves supplying them, 

 including especially the facial pneumogastric, spinal, 

 accessory, and external respiratory nerves, were classed 

 by Sir Charles Bell with the phrenic, as the respiratory 

 system of nerves. There appears, however, no propriety in 

 making a separate system of these nerves, since their mode 

 of action is not peculiar, and many besides them co- 

 operate in the respiratory acts. That which is peculiar 

 in the nervous influence, directing the extraordinary move- 

 ments of respiration, is, that so many nerves are com- 

 bined towards one purpose by the power of a distinct 

 nervous centre, the medulla oblongata. In other than 

 respiratory movements, these nerves may act singly or 

 together, without the medulla oblongata; but after it is 

 destroyed, no movement adapted to respiration can be per- 

 formed by any of the muscles, even though the part of the 

 spinal cord from which they arise be perfect. The phrenic 

 nerves, for example, are unable to excite respiratory move- 

 ment of the diaphragm when their connection with the 

 medulla oblongata is cut off, though their connection with 

 the spinal cord may be uninjured.* 



Effects of the Suspension and Arrest of Respiration. 



These deserve some consideration, because of the illustra- 

 tion which they afford of the nature of the normal processes 

 of respiration and circulation. When the process of respi- 

 ration is stopped, either by arresting the respiratory move- 



* The influence of the nervous system in respiration will be again 

 and more particularly considered in the section treating of the medulla 

 oblongata and pneumogastric nerves. 



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