RESPIRA TION 



2*7 



voice to become hoarse, and renders the sounding of high notes 

 an impossibility, owing to the want of power to make the vocal 

 cords tense. Stimulation of the vagus within the skull causes 

 contraction of the crico-thyroid muscle and increased tension of 

 the cords. Section or paralysis of the inferior laryngeal nerves 

 leads to loss of voice or aphonia, and dyspnoea (Fig. 127). Both 

 adductor and abductor muscles are paralyzed ; the vocal cords 

 assume their mean position the position they have in the dead 

 body and the glottis can neither be narrowed to allow of the 

 production of a note, nor widened during inspiration. It is said, 

 however, that young animals, in which the structures around 

 the glottis are more yielding than in adults, can still utter shrill 

 cries after section of the inferior laryngeals, the contraction of 

 the crico-thyroid muscle alone being able, while increasing the 

 tension of the cords, to draw them together. 



Interference with the connections on one side between the 

 higher cerebral centres and the medulla oblongata, as by rupture 

 of an artery and effusion of blood into the posterior portion of 

 the internal capsule (giving rise to hemiplegia, or paralysis of 

 the opposite side of the body), is not followed by loss of voice ; 

 the laryngeal muscles on both sides are still able to act. 



PRACTICAL EXERCISES ON CHAPTER III. 



i. Tracing of the Respiratory Movements in Man. Pass a tape 

 through the rings B of the stethograph shown in Fig. 128, and 

 then around the neck or over the shoulders, so as to support the 

 instrument on 

 the chest at 

 a convenient 

 height. Fasten 

 tapes to the 

 hooks and 

 tie them by 

 a slip - knot 

 round the 

 chest. The 

 tube E is con- 

 nected to a re- 

 cording tam- 

 bour, writing 

 on a drum. 

 Or use the 

 belt stetho- 

 graph or spiro- 

 graph of Fitz 

 (p. 2 1 8), fasten- 

 ing the elastic tube round the chest with the chain, and connecting 

 it with a tambour or the bellows recorder shown in Fig. 131. 

 Compare the extent of the excursion when the tube is adjusted at 

 different levels over the thorax and abdomen. 



FIG. 128. STETHOGRAPH. 



