726 NERVOUS SYSTEM. 



fibres is destroyed, these fibres after a time become degenerated. In old lesions of the 

 corpora striata, it has been shown that, when the white substance is injured upon one 

 side, there follow degeneration and atrophy of the fibres of the corresponding cerebral 

 peduncle and anterior pyramid of the medulla, and of the lateral portion of the spinal 

 cord upon the opposite side. This important fact illustrates the connection between the 

 lateral columns of the cord and the anterior pyramids of the medulla oblongata, the 

 decussation of the anterior pyramids, and the passage of fibres from the anterior pyra- 

 mids to the corpora striata, in the substance of the cerebral peduncles. 



Functions of the Medulla Oblongata. 



It is hardly necessary to discuss the functions of the medulla oblongata as a conductor 

 of sensory impressions and of motor stimulus to and from the brain. We know that there 

 is conduction of this kind from the spinal cord to the ganglia of the encephalon, and this 

 must take place through the medulla; a fact which is inevitable, from its anatomical rela- 

 tions, and which is demonstrated by its section in living animals. Nor is it necessary to 

 dwell upon its general properties, in which it resembles the spinal cord, at least as far as 

 has been demonstrated by experiments upon living animals or upon animals just killed. 

 It is difficult to expose this part in the higher classes of animals, but experiments show 

 that it is sensitive on its posterior surface and insensible in front. The difficulty of ob- 

 serving the phenomena which follow its irritation in living animals has rendered it im- 

 possible to determine the limits of its excitability and sensibility as exactly as has been 

 done for the different portions of the cord. 



It is also somewhat difficult to determine whether the action of the medulla itself, in 

 its relations to motion and sensation, be crossed or direct. As regards conduction from 

 the brain, the direction is sufficiently well shown by cases of cerebral disease, in which 

 the paralysis, in simple lesions, is always on the opposite side of the body. 



The action of the medulla as a reflex nerve-centre depends upon its gray matter. 

 When this gray substance is destroyed, certain of the important reflex functions are 

 instantly abolished. From jts connections with various of the cranial nerves, we should 

 expect it to play an important part in the movements of the face, in deglutition, in the 

 action of the heart and of various glands, etc., important points which will be fully con- 

 sidered in their appropriate place. Its most striking function, however, is in connection 

 with respiration. 



Connection of the Medulla Oblongata with Respiration. In 1809, Legallois made a 

 number of experiments upon rabbits, cats, etc., in which he showed that respiration 

 depends exclusively upon the medulla oblongata and not upon the brain, and he farther 

 located the part which presides over this function at the site of origin of the pneumogastric 

 nerves. Flourens, in his elaborate experiments upon the nerve-centres,, extended the 

 observations of Legallois, and limited the respiratory centre in the rabbit, between the 

 upper border of the roots of the pneumogastrics and a plane situated about a quarter of 

 an inch below the lowest point of origin of these nerves ; these limits, of course, varying 

 with the size of the animal. Following these experiments, Longet has shown that the 

 respiratory nervous centre does not occupy the whole of the medulla included between 

 the two planes indicated by Flourens, but that it is confined to the gray matter of the 

 lateral tracts, or the intermediary fasciculi. This was demonstrated by the fact that 

 respiration persists in animals after division of the anterior pyramids and the restiform 

 bodies. Subsequently, Flourens still farther restricted the limits of the respiratory centre 

 and fully confirmed the observations of Longet. 



The portion of the medulla oblongata above indicated presides over the movements 

 of respiration and is the true respiratory nerve-centre. Nearly all who have repeated 

 the experiments of Flonrens have found that the spinal cord may be divided below the 

 medulla oblongata, and that all of the encephalic ganglia above may be removed, re- 



