GENERAL ARRANGEMENT OF THE PHONATING ORGANS 545 



of the true vocal cords more effective. Special use is made of this 

 mechanism, in conjunction with the closure of the epiglottis, whenever 

 large amounts of air are to be temporarily retained in the lungs, or 

 when, as in running, the outflow of the expiratory air is to be retarded. 

 Thirdly, inasmuch as their mucous covering contains numerous mucous 

 and serous glands, it is also believed that they furnish the moisture 

 necessary to keep the vocal cords in a 

 proper condition for vibration. This secre- 

 tion is temporarily retained in the capillary 

 space between the true and false cords and 

 is in this way protected against evaporation. 

 In some of the lower animals, these spaces 

 which are called the ventricles of Morgagni, 

 are very commodious and are constructed 

 in such a way that they may serve as reso- 

 nating chambers. This peculiarity in their 

 general arrangement has led to the belief 

 that they tend to augment the vibration of 

 the true vocal cords. 



The Tension of the True Vocal Cords. 

 — The thyroid and cricoid cartilages arti- 

 culate by means of a simple bilateral joint, 

 the axis of which is placed transversely. 

 Arising upon the anterolateral aspect of 

 the cricoid, a small conical muscle, known as 

 the cricothyroid, passes upward and back- 

 ward to be inserted upon the lower edge 

 of the alse of the thyroid (Fig. 270). Its 

 function is to diminish the height of the 

 space between the inferior border of the 

 thyroid and the upper border of the cricoid 

 cartilages. This end it attains by depress- 

 ing the former and raising the latter. The 

 result of this movement is made evident 

 immediately if it is noted that these car- 

 tilages are hinged posteriorly (R) and that 

 the arytenoids (A), which are situated 

 transversely upon the tips of the cricoid pro- 

 cesses, are thereby moved farther backward. 

 It will be remembered that the vocal cords 

 (VC) are attached to the anterior tips of 



these cartilages and extend from here directly across the cavity to be 

 inserted upon the anterior wall of the larynx. Obviously, therefore, 

 since the approximation of the thyroid and cricoid cartilages increases 

 the distance between the vocal processes of the arytenoids and the 

 anterior wall of the larynx, these bands must be put on the stretch. 

 Thus, it is evident that the aforesaid muscle serves as the tensor of 



35 



Fig. 270. — Lateral View 

 OF Larynx to Illustrate the 

 Action of the Cricothyroid 

 Muscle. 



H, hyoid bone; M, thyro- 

 hyoid membranes; PA, po- 

 mum Adami; T, thyroid carti- 

 lage; C, cricoid cartilage; Tr, 

 trachea; CT, cricothyroid 

 muscle; P, vertical plate of 

 cricoid with (A) arytenoid 

 cartilages placed transversely 

 upon its articulating processes; 

 VC, vocal cords; R, imaginary 

 center of rotation of cricoid. 

 When cricothyroid muscle con- 

 tracts, T and C are brought 

 closer together, while A is 

 forced away from PA. 



