342 INNERVATION. [CHAP. XI. 



one part are so readily affected by any change in those of the other. 

 Thus, the olivary columns, which form the central and most essen- 

 tial part of the medulla oblongata, extend upwards through the 

 mesocephale to the optic thalami ; and the anterior pyramids form 

 an intimate connexion not only with the vesicular matter of the 

 mesocephale, but, to a great extent,, with that of the corpora striata. 

 All these parts taken together, with the quadrigeminal tubercles, 

 will be found to be the centre of the principal mental nervous 

 actions, and of certain physical actions which are very essential to 

 the integrity of the ceconomy. 



The office of the nerves which arise from this segment of the 

 encephalon throws light upon its function. These nerves are 

 partly destined for respiration, partly for deglutition, and partly 

 also for acts of volition and sensation. 



Destruction of the medulla oblongata is followed by the imme- 

 diate cessation of the phenomena of respiration ; and this takes 

 place whether it be simply divided, or completely removed. When 

 an animal is pithed, he falls down apparently senseless, and ex- 

 hibiting only such convulsive movements as may be due to the 

 irritation of the medulla by the section, or such reflex actions as 

 may be excited by the application of a stimulus to some part of 

 the trunk. 



If, in an animal which breathes without a diaphragm, as in a 

 bird or reptile, the spinal cord be gradually removed in successive 

 portions, proceeding from below, up to within a short distance of 

 the medulla oblongata, loss of motor and sensitive power takes place 

 successively in the segments of the body with which the removed 

 portions of the cord were connected. But the animal still retains 

 its power of perceiving impressions made on those parts of the body 

 which preserve their nervous connexion with the medulla oblongata, 

 and continues to exercise voluntary control over the movements 

 of those parts. The movements of respiration go on, and deglu- 

 tition is performed. The higher senses are unimpaired.* 



These phenomena are sometimes observed in man in such cases 

 as that alluded to in a former page ; where from injury to the spinal 

 cord in the neck, below the origin of the phrenic nerve, the patient 

 appears as a living head with a dead trunk. The sensibility and 

 motor power of the head are perfect; respiration goes on par- 

 tially, and deglutition can be readily performed. The senses and 

 the intellectual faculties remain for a time unimpaired. 



Irritation of any part of the medulla oblongata excites con- 

 * Flourens, p. 179. 



