676 OF THE FUNCTIONS OF THE NERVOUS SYSTEM. 



in the individual that executes it, is sufficiently proved by the existence of such 

 a combination in various automatic movements, most essential to the mainte- 

 nance of the organic functions, which are performed with the utmost regularity, 

 not only without our bestowing any volitional effort upon them, but also under 

 circumstances which indicate that not even our consciousness has any share in 

 developing or directing them. Such are the ordinary and extraordinary move- 

 ments of Respiration, the movements of Deglutition and Defecation, &c. 



710. Medulla Oblongata. The cranial prolongation of the Spinal cord, 

 which is distinguished by this appellation, has been regarded by some Physiolo- 

 gists as the peculiar seat of vitality ; since, although the other Encephalic masses 

 may be withdrawn from above, and nearly the whole of the Spinal Cord may 

 be removed from below, without the destruction of life, yet a complete stop is 

 put to the current of vital action when the Medulla Oblongata is destroyed. 

 [The arrest of vital action does not take place in frogs, or in other animals 

 that respire largely by the general surface, as for instance amphibia and reptilia, 

 for in them life continues for weeks, or even months, after complete removal of 

 the Medulla Oblongata; circulation, digestion, and secretion going on with an 

 activity but little impaired; death finally occurring from the diminution of the 

 respiratory functions. 1 ED.] But the dependence of the vital activity of the 

 body generally upon the functional integrity of this part of the nervous system 

 is simply consequent upon the fact that the Medulla Oblongata contains the gan- 



Fig. 176. Fig. 177. 



Anterior view of the medulla ob- Posterior view of the medulla oblongata : pp. Posterior pyra. 



longata: p, p. Pyramidal bodies, mids, separated by the posterior fissure. rr. Restiform 



decussating at d. o, o. Olivary bo- bodies, composed of cc, posterior columns, and dd, lateral 



dies, r, r. Restiform bodies, a, a. part of the antero-lateral columns of the cord. aa. Olivary 



Arciform fibres, v. Lower fibres of columns, as seen on the floor of the fourth ventricle, separated 



the Pons Varolii. by , the median fissure, and crossed by some fibres of origin of 



nn, the seventh pair of nerves. 



glionic centre of the Respiratory movements; upon the continuance of which, as 

 already shown (CHAP. x. SECT. 3), the continuance of the Circulation is depend- 

 ent, and, with this, the maintenance of the Organic functions generally. In no 

 other essential respect does the Medulla Oblongata differ from the Medulla Spi- 

 nalis than in its ministration to certain classes of reflex movements which are 



1 [Vide Phil. Med. Examiner, N. S., Vol. viii., No. xcii., in which will be found an ac- 

 count of the experiments of Dr. 13rown-Se"quard upon this subject.] 



