THE VISCERAL AND GUSTATORY APPARATUS 



237 



in the lower part of the medulla oblongata (the area visceralis of 

 Fig. 43, p. 111). 



In the ordinary breathing of mammals the act of inspiration 

 is effected by an upward and outward movement of the ribs and 

 a downward movement of the diaphragm. Now, if the spinal 

 cord be cut through at the level of the seventh cervical nerve the 

 respiratory movement of the ribs is entirely abolished, though 

 the movements of the diaphragm go on as usual. The continuity 



Dorsal motor X 



nucleus 

 Nucleus of fascic. solitarius 



Fasciculus solitarius 

 Vagus ganglion 

 Vagus nerv 

 Tr. solitario-spinal 



Sympathetic ganglia 



Lung 

 Intercostal nerve. 



Intercostal muscle 

 Phrenic nerve 



Diaphragm 



Respiratory center 



Fig. 112. Diagram of the nervous mechanism of respiration, 

 from Ram6n y Cajal.) 



(Modified 



of the thoracic motor nerves which innervate the intercostal 

 muscles with their centers of origin in the spinal cord is undis- 

 turbed by this operation, yet they can no longer be coordinated 

 in the respiratory act. If in another animal the spinal cord be 

 divided at the level of the third cervical nerve, i. e., above the 

 level of origin of the phrenic nerve, the respiratory movement - < if 

 both the ribs and the diaphragm cease, even though the spinal 

 cord below the section is intact and its connection with the 

 peripheral respiratory apparatus is undisturbed. These experi- 



