I826 HUMAN ANATOMY. 



icroscopic sections that fibres were often inserted obliquely into the cord and into 

 the end o^ the local process. There was, however, much variation, and m some 

 cases no such fibres were found. Our own observations incline us to look upon such 

 possible, but probably in the ordinary larynx they are few and far between. 

 JS Portion ( Fig 1554) is a thin membrane on the outer side of the ven- 

 de u h s^fi ^ s^inK^ard and backward towards the aryepiglottic fold 

 S nc ew fibres are, or may be, found in the false cord, and some occasionally arch 

 over the ventricle. The external portion is very irregular and inclined to give off 

 aberrant bundles. The superior thyro-arytenoid is a common one. It Arises from 

 the inner side of the ala of the thyroid, near the top, a little outside of the notch, and 

 runs downward and backward to the top and anterior aspect of the vocal process 

 resting on the outer side of the external part of the thyro-arytenoid and crossing it 

 at right angles. It consists of long parallel fibres and varies much in size. 

 tkyrt^iglottu muscle is simply fibres of the system of the thyro-arytenoid that pass 

 vardTo the side of the epiglottis. We incline to 



FIG. 1555. 



Body of hyoid 

 bone (cut) 



Epiglottis 



Mass of fat 



I M,< :il . old 



Thyroid cartilage 

 True vocal i <>nl 

 Thyro-arytenoideus 

 interims 



thyroideus V 



Anterior arch of cricoid I 

 cartilage 



Tracheal 

 cartilages 



Greatei hycid 

 cornu 



Superior thyroid 

 cornu 



Ventricle of larynx 

 .Arytenoid cartilage 



.Crico-arytenoideus 



lateralis 

 push-rior arch of 



cricoid cartilage 

 Line of cut mucosa 



chea 



tending from the side of the 

 arytenoid to the epiglottis in 

 the edge of the fold a part 

 of this same system. 



Action. That of the in- 

 ternal part of the thyro-aryte- 

 noid is to relax the vocal cords 

 by approximating their ends ; 

 if, however, the fibres inserted 

 into the cords be worth consid- 

 ering, this action must be modi- 

 fied by the stretching of parts 

 of the cords while others are 

 relaxed. The irregularity of 

 this arrangement is quite in har- 

 mony with the endless variations 

 of the human voice. The shape 

 of the walls below the true cords 

 must also be modified by the 

 swelling of the contracting mus- 

 cle. The action of the outer 

 portion of this muscle must be 

 in the main that of a constrictor 

 of the supraglottir region. It is possible that when the cords are abducted some of 

 the fibres inserted into the muscular processes may act as adductors. 



The arytenoid muscle (m. intcrarytaonoidcus) is a mass of fibres running trans- 

 versely between the hollows on the posterior surfaces of the arytenoid cartilages, which 

 it fills i Fig. 1553 ). There is usually a superficial oblique part of this muscle which, 

 u lu-n well developed, is formed by two bands crossing each other like the arms of an 

 X placed on its side. Ka< h arm starts from the muscular process of the arytenoid and 

 to tin- Mimmit of the arytenoid of the opposite side. Here it may end or be 

 continuous \\ith the til ties of the aryepiglottic muscle, which ascend to the epiglottis. 

 One or both arms may be wanting, and this part may be more or less fused with the 

 deeper transverse fibn 



am. It draws the arytenoid cartilages together, and is, moreover, an im- 

 portant part of the sphincter-like arrangement. 



Vessels. The arteries are the superior laryngeal and the crico-thyroid from 

 the superior thyroid arterv and the inferior laryngeal from the inferior thyroid artery. 

 The superior l.u \n-.al pierces the thyro-hyoid membrane some 5 mm. from the 

 superior horn of the thyroid and about midway between the top and the bottom. 

 After giving oti an epiglottic branch, which on its way supplies the areolar tissue 

 anterior to the epiglottis, the vessel runs downward and backward under cover of the 

 ala of the thyroid in its distribution in the upper part of the larynx. The crico- 



Sagittal section of larynx from within ; mucous membrane has been 

 removed from vocal cord to lower level of cricoid cartilage. 



