i826 



HUMAN ANATOMY. 



Body of hyoid 

 bone (cut) 



Epiglottis 



Mass of fat 



False vocal cord 



Thyroid cartilage 



True vocal cort 



Thyro-arytenoideus 

 intermis 



Crico-thyroideus 



Anterior arch of cricoid 

 cartilage 



Tracheal 

 cartilages 



Greater hyoid 

 cornu 



Superior thyroid 

 cornu 



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

 the end of the vocal process. There was, however, much variation, and in some 

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

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

 The external portion (Fig. 1554) is a thin membrane on the outer side of the ven- 

 tricle, with its fibres spreading upward and backward towards the aryepiglottic fold. 

 Some few 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. The 

 thyro-epighttic muscle is simply fibres of the system of the thyro-arytenoid that pass 

 upward to the side of the epiglottis. We incline to consider the aryepiglottic muscle 



(Fig. 1554) — a little bundle ex- 

 FiG 1555. 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 supraglottic 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. interarvtaenoideus) is a mass of fibres running trans- 

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

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

 when well developed, is formed by two bands crossing each other like the arms of an 

 X placed on its side. Each arm starts from the muscular process of the arytenoid and 

 crosses to the summit of the arytenoid of the opposite side. Here it may end or be 

 continuous with the fibres 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 fibres. 



Action. — 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 artery and the inferior laryngeal from the inferior thyroid artery. 

 The superior laryngeal 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 off an epiglottic branch, which on its way supplies the areolar tissue 

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

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



Ventricle of laiynx 

 Arytenoid cartilage 



Crico-arytenoideus 



lateralis 

 Posterior arch of 



cricoid cartilage 

 Line of cut mucosa 



Trachea 



Sagittal section of larynx from within ; mucous membrane has been 

 removed from vocal cord to lo^er level of cricoid cartilage. 



