THE MEDULLA OBLONGATA. 509 



accomplished by reflex action ; but it becomes impossible as soon as 

 this part is removed or seriously injured. The muscular combinations 

 necessary to deglutition cannot take place, except under the influence 

 of the medulla as a nervous centre. 



This action may consequently be performed, in man, after all sensi- 

 bility and voluntary power have disappeared. In cases of compression 

 of the brain from injury or disease, when the individual is in a state of 

 complete unconsciousness, and even when the respiration is diminished 

 in frequency, solid or liquid food, if carried into the upper part of the 

 pharynx, may be successfully swallowed by the ordinary movements of 

 deglutition. When this process is no longer possible, or is accompanied 

 by choking or regurgitation, it indicates that the medulla has become 

 seriously affected, and that death is probably near at hand. 



The medulla is furthermore connected with the act of phonation. The 

 production of a vocal sound is usually the result of a voluntary impulse 

 derived from the operation of the cerebral hemispheres. It is sometimes 

 also a purely emotional act, originating in the excitement of the tuber 

 annulare, and without any reasonable or intelligent motive. But in 

 these cases its production is a secondary result, requiring the co-opera- 

 tion of other nervous elements, and its immediate centre is located in 

 the medulla. This is shown by the fact that a cry may still be produced 

 when the upper parts of the encephalon have been destroyed or removed, 

 and when an irritation is applied to the medulla alone. If a stilet be 

 introduced into the cranium of a frog, the cerebral hemispheres may 

 be broken up without producing any excitement of the vocal organs ; 

 but when the instrument touches the medulla, its contact is often fol- 

 lowed by a distinct and spasmodic cry. Yulpian has shown that a similar 

 effect may be produced in mammalians, after removal of the whole 

 encephalon excepting the medulla, by a reflex action. A cry is pro- 

 duced each time the integument of the foot is pinched by the blades of 

 a forceps. This sound, however, gives no indication of consciousness 

 or sensibility on the part of the animal. It is short, abrupt, and momen- 

 tary in duration, and is repeated only when the irritation is again applied 

 to the external parts. It is a purely mechanical effect of the tension of 

 the vocal cords and the sudden expulsion of air through the rima glot. 

 tidis. After the destruction of the medulla, on the other hand, no vocal 

 sound can be produced, and the same irritation of the integument is. 

 then followed only by the ordinary spasmodic movement of the limbs, 

 dependent on the reflex action of the spinal cord. 



In the exercise of the voice, therefore, the preliminary actions of in- 

 telligence, volition, or emotional excitement require the co-operation of 

 the cerebrum and the tuber annulare ; but the immediate mechanism by 

 which a vocal sound is produced in the larynx has its nervous centre in 

 the medulla oblongata. 



This part of the brain, with the adjoining part of the tuber annulare, 

 is also the direct source of the movements of articulation. It is the 

 gray substance of this region that gives origin to the hypoglossal and 



