THE BRAIN. 441 



interfered with and finally arrested as a secondary consequence, because 

 the blood is no longer arterialized ; but respiration is abolished at once r 

 as an immediate result of injury to the medulla. 



As the movements of respiration are performed by the consenta- 

 neous action of different muscles, the effect of an injury to the cerebro- 

 spinal axis will vary according to its locality. The respiratory move- 

 ments of the chest and abdomen are arrested by section of the cord 

 anywhere above the third cervical vertebra, since this paralyzes both 

 the diaphragm and the intercostal muscles. But movements of inspi- 

 ration, simultaneous with those of the chest and abdomen, are also 

 performed by the glottis ; and in most quadrupeds there is at the same 

 time an expansion of the nostrils, all associated with each other in the 

 act of respiration. If the spinal cord be divided at the third cervical 

 vertebra the movements of the chest and abdomen cease, but those of 

 the glottis and nostrils continue, since the nerves supplying these parts 

 are still in communication with the medulla oblongata. But destruc- 

 tion of the medulla arrests at the same instant all movements of respi- 

 ration, both in the trunk, the glottis, and the face. 



The medulla accordingly is a centre from which the whole respiratory 

 apparatus derives its stimulus, and in man, quadrupeds, and birds it is 

 the most important part of the brain for the immediate preservation 

 of life. 



The more exact location of the respiratory centre was investigated 

 by Flourens * by making transverse sections of the medulla at different 

 parts of its length, and observing the effect produced. The result 

 showed that such injuries, inflicted just behind the point of emergence 

 of the pneumogastric nerves, destroyed all the movements of respira- 

 tion together. Below this point, the movements of the chest and abdo- 

 men were stopped, but those of the nostrils and glottis continued ; above 

 it, the movements of the nostrils were arrested, while those of the 

 chest and abdomen went on. 



Flourens subsequently f limited the position of this centre still more 

 closely. In rabbits it occupies a space of about 2.5 millimetres on each 

 side the median line, situated at the lower end of the fourth ventricle, 

 a little in advance of the divergence of the posterior pyramids, and 

 just at the point of gray substance formed by the ala cinerea. A. 

 section of the medulla at this spot, with a double-edged knife only 

 5 millimetres wide, or its perforation at the same point with a sharp- 

 edged canula not more than 3 millimetres in diameter, caused imme- 

 diate stoppage of respiration ; while this effect was not produced by 

 similar injuries either above or below. This spot, which contains the 

 nervous centre of respiration, corresponds, in man, on the front of the 

 medulla oblongata, with the upper end of the decussation of the ante- 



* Recherches Experimentales sur les Proprietes et les Fonctions du Systeme Xer- 

 veux. Paris, 1842, pp. 196-204. 



f Comptes Rendus de 1' Academic des Sciences. Paris, 1858, tome xlvii., p. 803. 



