74 THIRD REPORT — 1833. 



might be removed, for though the raisjng of the ribs ceased, 

 the action of the diaphragm continued as long as the origin of 

 the phrenic nerve remained uninjured. In frogs, all the spinal 

 medulla may be destroyed, except the portion, whence spring the 

 nerves supplying the hyoideal apparatus. Every part of the 

 spinal marrow may be removed in fishes without affecting re- 

 spiration ; for all the nerves distributed to the respiratory organs 

 of fishes have their origin in the medulla oblongata. It is 

 hence apparent that the spinal marrow exercises only a variable 

 and relative action on the I'espiratory function, in the different 

 classes of vertebrated animals. In descending from the higher 

 to the lower points of this scale, the spinal marrow is seen pro- 

 gressively to disengage itself from cooperation in these move- 

 ments, while the medulla oblongata tends more and more to 

 concentrate them in itself, till in fishes the proper functions of 

 the two meduUge show themselves completely distinct, the spinal 

 ministering to locomotion and sensation, and the oblongata to re- 

 spiration. The medulla oblongata is, then, the "premier mo- 

 teur " or the exciting and regulating principle of the inspiratory 

 movements in all classes of vertebrated animals ; besides par- 

 ticipating, by virtue of its continuity with the spinal marrow, in 

 the proper functions of that organ. From a second series of 

 experiments, M. Flourens concludes that there exists a point 

 in the nervous centres at which the section of those centres 

 produces the sudden annihilation of all the inspiratory move- 

 ments ; and that this point corresponds with the origin of the 

 eighth pair of nerves, commencing immediately above, and ending 

 a little below, that origin, — a result precisely agx'eeing with that 

 obtained by Legallois. 



Spinal Marrow. — It is apparent, that the functions of the 

 three grand divisions of the nervous system, already described, 

 have not yet been distinctly and fully ascertained. Our know- 

 ledge of those, which next fall under survey, is more definite 

 and substantial. The vital offices of the spinal medulla — re- 

 garded by Legallois as the mainspring of life, and as alone re- 

 gulating the actions of the heart and nobler organs, — are now 

 reduced to conveying to the muscles the motive impulse of voli- 

 tion, and to propagating to the sensorium commune, impressions 

 made on the external senses. It is not invested with the power 

 possessed by the cerebrum and cerebellum, and perhaps by the 

 medulla oblongata, of spontaneously originating muscular mo- 

 tions. It is mainly, if not exclusively, a conductor; a medium 

 of communication between the brain and the external instru- 

 ments of locomotion and sensation. Flourens, indeed, conjee- 



