506 THE BRAIN. 



In man, quadrupeds, and birds, it is a vital point; since in them the 

 function of respiration, over which it presides, is necessary for the con- 

 tinuance of life from one moment to another. 



The fact that sudden death may be produced by injury of the cerebro- 

 spinal axis in this region was known to Galen, who described the method 

 of killing an animal by section of the spinal cord " at the upper cervical 

 vertebrae." The respiratory movements of the chest and abdomen are 

 however necessarily arrested by section of the cord anywhere above 

 the third cervical vertebra, since this paralyzes at once both the dia- 

 phragm and the intercostal muscles. But movements of inspiration, 

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

 by the glottis ; and in most of the 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 verte- 

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

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

 are still in communication with the medulla oblongata. Destruction 

 of the medulla itself, on the other hand, arrests at the same instant all 

 movements of respiration, both in the trunk, the glottis, and the face. 

 It is, therefore, a centre from which the respiratory apparatus in general 

 derives its stimulus. 



The more exact location of this centre was investigated by Flourens 1 

 by making transverse sections of the medulla at different parts of its 

 length, and observing the effect produced upon respiration. The result 

 showed that injuries of this kind, inflicted just behind the point of 

 emergence of the pneumogastric nerves, destroyed at once all the move- 

 ments of respiration together. Below this point the movements of the 

 chest and abdomen 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. 



Similar experiments performed by Longet show that the respiratory 

 centre does not extend through the entire thickness of the medulla; 

 since either the anterior pyramids in front or the restiform bodies 

 behind may be destroyed without putting a stop to respiration ; while a 

 lesion passing through the intermediate layer at once causes its sus- 

 pension. Flourens subsequently 2 limited the position of this centre 

 still more closely, and found that 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 



1 Kecherches Experimentales sur les Proprietes et les Fonctions du Systeme 

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



2 Comptes Kendu de 1' Academic des Sciences. Paris, 1858, tome xlvii. p. 803. 



