HO HAND-BOOK OF PHYSIOLOGY. 



obvious that all impressions passing to and fro between the brain and the 

 spinal cord and all nerves arising below the pons, must be transmitted 

 through it. 



2. As a nerve-centre by which impressions are transferred or reflected, 

 the medulla oblongata also resembles the spinal cord; the only difference 

 between them consisting of the fact that many of the reflex actions per- 

 formed by the former are much more important to life than any per- 

 formed by the spinal cord. 



Demonstration of Functions. It has been proved by repeated 

 experiments on the lower animals that the entire brain may be gradually 

 cut away in successive portions, and yet life may continue for a consider- 

 able time, and the respiratory movements be uninterrupted. Life may 

 also continue when the spinal cord is cut away in successive portions from 

 below upward as high as the point of origin of the phrenic nerve. In 

 Amphibia, the brain has been all removed from above, and the cord, as 

 far as the medulla oblongata, 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 

 wounded in its central part, opposite the origin of the pneumogastric 

 nerves, the respiratory movements cease, and the animal dies asphyxi- 

 ated. And this effect ensues even when all parts of the nervous system, 

 except the medulla oblongata, are left intact. 



Injury and disease in men prove the same as these experiments on 

 animals. Numerous instances are recorded in which injury to the me- 

 dulla oblongata has produced instantaneous 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. 



SPECIAL CENTRES. 



(1.) Respiratory. The centre whence the nervous force for the pro- 

 duction of combined respiratory movements appears to issue is in the in- 

 terior of that part of the medulla oblongata from which the pneumo- 

 gastric nerves or Vagi arise. The vagi themselves, indeed, are not essen- 

 tial to the respiratory movements; for both may be divided without more 

 immediate effect than a retardation of these movements. But in this 

 part of the medulla oblongata is the nerve-centre whence the impulses 

 producing the respiratory movements issue, and through which impulses 

 conveyed from distant parts are reflected. 



The wide extent of connection which belongs to the medulla oblongata 

 as the centre of the respiratory movements, is shown by the fact that 

 impressions by .mechanical and other ordinary stimuli, made on many 

 parts of the external or internal surface of the body, may modify, i.e., in- 



