516 THE NERVOUS SYSTEM. 



this part is invaded. This is not because the integrity of 

 the pneumogastric nerves is essential to the respiratory 

 movements ; for both these nerves may be divided without 

 more immediate effect than a retardation of these move- 

 ments. The conclusion, therefore, may safely be, that 

 this part of the medulla oblongata is the nervous centre 

 wherein the impulses producing the respiratory move- 

 ments chiefly originate, and whence they issue in rhythm 

 and adaptation.* 



The power by which the medulla oblongata governs and 

 combines the action of various muscles for the respiratory 

 movements, is an instance of the power of reflexion, which 

 it possesses in common with all nervous centres. Its 

 general mode of action, as well as the degree to which 

 the mind may take part in respiration, and the number of 

 nerves and muscles which, under the governance of the 

 medulla oblongata, may be combined in the forcible respi- 

 ratory movements, have been already briefly described (see 

 p. 236, et seq.). That which seems most peculiar in this 

 centre of respiratory action is its wide range of connection, 

 the number of nerves by which the centripetal impression 

 to excite motion may be conducted, and the number and 

 distance of those through which the motor impulse may be 

 directed. The principal centripetal nerves engaged in 

 respiration are the pneumogastric, whose branches supply- 

 ing the lungs appear to convey the most acute impression 

 of the ''necessity of breathing." When they are both 



* Dr. Brown -Sequard has of late brought forward some important 

 evidence, to show that the impulses leading to the respiratory move- 

 ments do not originate exclusively in the medulla oblongata, but that 

 they issue also from all the other incito-motory parts of the cerebro- 

 spinal axis and from the grey matter which connects those parts with 

 the motor nerves going to the respiratory muscles. The influence of 

 the medulla oblongata upon the respiratory movements is, however, 

 undoubtedly so great, that there probably need be no hesitation in 

 adopting the general conclusion stated above. 



