REPORT ON THE PHYSIOLOGY OF THE NERVOUS SYSTEM. 91 



8. The medulla oblongata exercises the office of originating 

 and regulating the motions essential to the act of respiration. 

 By virtue of its continuity with the spinal marrow, it also par- 

 ticipates in the functions of that division of nervous matter. 



9. The function of the spinal cord is simply that of a con- 

 ductor of motive impulses, from the brain to the nerves supply- 

 ing the muscles, and of sensitive impressions from the surface 

 of the body to the sensorium commune. These two vital 

 offices reside in distinct portions of the spinal medulla, — the 

 propagation of motion in its anterior columns, the transmission 

 of sensations in its posterior columns. There is no necessary 

 dependence of the motions of the heart, and the other invo- 

 luntary muscles, on the spinal marrow. 



10. The nerves are comprehended in the four following 

 classes : — I. Nerves simply of motion ; II. Of motion and sen- 

 sation ; III. Of three of the senses ; IV. The ganglionic sy- 

 stem. 



I. The nerves of motion are the third, fourth, sixth, portio 

 dura of the seventh, and the ninth. It is not ascertained whe- 

 ther the glossopharyngeal and spinal accessory nerves belong to 

 this or to the second class. 



11. The function of ministering both to motion and sensation 

 is possessed by the fifth pair of cerebral nerves, and by the 

 spinal nerves, which agree precisely in anatomical composition. 

 The par vagum, however, which is one of the irregular nerves, 

 has also a twofold endowment. 



III. This division comprises the first and second pairs, and 

 the portio mollis of the seventh pair. These nerves are insen- 

 sible to ordinary stimulants, and possess an exclusive sensibility 

 to their respective objects, — viz. odorous matter, light, and aei-ial 

 undulations. 



IV. The system of the great sympathetic nerve, and its as- 

 sociated plexuses and gangUa. 



