406 THE NERVOUS SYSTEM. 



rupted. Life may also continue when the spinal cord is cut 

 away in successive portions from below upwards as high as the 

 point of origin of the phrenic nerve, or in animals without a 

 diaphragm, such as birds or reptiles, even as high as the me- 

 dulla oblongata. In Amphibia, these two experiments have 

 been combined ; the brain being all removed from above, and 

 the cord from below ; and so long as the medulla oblongata 

 was intact, respiration and life were maintained. But if, in 

 any animal, the medulla oblongata is wounded, particularly if 

 it is w r ounded in its central part, opposite the origin of the 

 pneumogastric nerves, the respiratory movements cease, and 

 the animal dies as if asphyxiated. And this effect ensues even 

 when all parts of the nervous system, except the medulla ob- 

 longata, are left intact. 



Injury and disease in men prove the same as these experi- 

 ments on animals. Numerous instances are recorded in which 

 injury to the human medulla oblongata has produced instanta- 

 neous death ; and, indeed, it is through injury of it, or of the part 

 of the cord connecting it with the origin of the phrenic nerve, 

 that death is commonly produced in fractures and diseases 

 with sudden displacement of the upper cervical vertebrae. 



The centre whence the nervous force for the production of 

 combined respiratory movements appears to issue is in the 

 interior of that part of the medulla oblongata from which the 

 pneumogastric nerves arise; for with care the medulla ob- 

 longata may be divided to within a few lines of this part, and 

 its exterior may be removed without the stoppage of respira- 

 tion; but it immediately ceases when 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 retarda- 

 tion of these movements. The conclusion, therefore, may safely 

 be, that this part of the medulla oblongata is the nervous 

 centre whereby the impulses producing the respiratory move- 

 ments are reflected. 



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 mus- 

 cles which, under the governance of the medulla oblongata, 

 may be combined in the forcible respiratory movements, have 

 been already briefly described (see p. 184, 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 



