PHONATION 549 



death. Account must also be taken of the fact that the accompanying 

 paralysis of the esophageal musculature leads to an accumulation of 

 food and fluids which eventually find their way into the respiratory 

 channel. Consequently, the division of the inferior laryngeal nerves 

 paralyzes that mechanism by means of which the lungs are ordinarily 

 protected against foreign bodies and injurious emanations. Suffo- 

 cation or pneumonic conditions are the usual outcome of this defect. 

 Very similar results m^y be obtained by the division of the superior 

 laryngeal nerves, because this procedure blocks those afferent impulses 

 which normally evoke the act of coughing, thereby dislodging the 

 foreign material from the larynx. 



By selecting the highway of the vagus, these sensory impulses 

 eventually reach the nucleus of this nerve in the medulla, whence they 

 are relayed to other centers and finally to the motor area in the cere- 

 bral cortex. Those movements of the larynx which are associated 

 with respiration, are automatically controlled by a center situated in 

 the medulla and closely alhed to the respiratory center.^ Motor 

 points for the laryngeal muscles have been isolated by Krause^ in 

 the gyrus praefrontalis. It will be pointed out later on during the 

 discussions upon cerebral localization, that these motor points are 

 under the control of a psychic center for phonation and speech, which 

 is situated in part in the left inferior frontal convolution. 



CHAPTER XLIV 

 PHONATION 



In order to be able to produce a sound, it is necessary to be in 

 possession of a vibrating body the constituents of which may be set into 

 an alternating motion by some external force. In the higher animals, 

 the chief vibrating bodies are the vocal cords, while the power to make 

 them oscillate is most commonly suppHed by an expiratory blast of air 

 which may be softened or intensified by muscular activity. Moreover, 

 since these expiratory blasts are directed not only against the vocal 

 cords but also against other mucous folds and membranous septa, 

 noises and sounds of practically all descriptions may be obtained. 

 It is true, however, that those sounds which are ordinarily coordinated 

 into speech, are chiefly dependent upon the vibration of the vocal 

 cords, while the parts above and below them serve merely to modify 

 the primary sound. In this regard man possesses a decided advantage, 

 because the different parts of the human larynx are more delicately 

 adjusted and are under the direct control of an intricate system of motor 



1 Grossman, Zentralbl. fiir Physiol., iii, 1889. 



2 Archiv fiir Anat. und Physiol., 1884. 



