444 THE NERVOUS SYSTEM. 



combinations cannot take place, except under the influence of the 

 medulla as a nervous centre. 



Deglutition may consequently be performed, in man, after conscious 

 sensibility and voluntary power have disappeared. In compression of 

 the brain from injury or disease, when the individual is completely 

 unconscious, and even when respiration has become diminished in 

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

 pharynx, may be successfully swallowed by the ordinary movements. 

 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 phonation. A vocal 

 sound is usually caused by a voluntary impulse from the cerebral 

 hemispheres. It may also be a purely emotional act, without any 

 reasonable or intelligent motive. But in both cases its actual pro- 

 duction is a secondary result, requiring special nervous combinations, 

 the immediate centre of which is located in the medulla. This is 

 shown by the fact that a cry may still be produced, under an irrita- 

 tion applied to the medulla, when the upper parts of the encephalon 

 have been removed. 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 the contact of the instru- 

 ment with the medulla is often followed by a spasmodic cry. Yulpian 

 has shown that a similar effect may be produced in mammalians by 

 reflex action, after removal of the whole encephalon excepting the 

 medulla ; a cry being produced each time the foot is pinched by a for- 

 ceps. This sound, however, gives no indication of consciousness or 

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

 ary, and is repeated only when the irritation is again applied to the 

 external parts. After destruction of the medulla, on the other hand, 

 no vocal sound can be produced, and irritation of the integument is 

 followed only by the ordinary movement of the limbs, dependent on 

 reflex action of the spinal cord. 



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

 intelligence, volition, or emotional excitement require the cooperation 

 of other parts of the encephalon ; but the immediate mechanism by 

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

 oblongata. 



The medulla oblongata, with the adjoining part of the tuber annu- 

 lare, 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 facial nerves distributed to the muscles of the tongue and lips, and 

 to the motor fibres of the pneumogastric nerve, which regulate the 

 condition of the rima glottidis. Disease or injury in this situation, 

 sufficient to impair nervous action, consequently makes articulation 

 difficult or impossible. This affection is quite distinct from " aphasia," 

 which is of cerebral origin, and in which the external mechanism of 



