496 VOICE AND SPEECH. 



to increase the efficiency of certain of the other intrinsic 

 muscles. 1 



Lateral Crico-arytenoid Muscles. These muscles are 

 situated in the interior of the larynx. They arise from 

 the sides and superior borders of the cricoid cartilage, pass 

 upward and backward, and are attached to the base of the 

 arytenoid cartilages. By dividing all of the filaments of the 

 recurrent laryngeal nerves except those distributed to these 

 muscles, and then galvanizing the nerves, Longet has shown 

 that they act to approximate the vocal chords and constrict 

 the glottis, particularly in its interligamentous portion. 2 

 These muscles, with the arytenoid, act as constrictors of the 

 larynx. 



Thyro-arytenoid Muscles. It is sufficiently easy to indi- 

 cate the relations and attachments of these muscles, but their 

 mode of action is more complex and difficult of comprehen- 

 sion. When we come to study the conditions of the vocal 

 chords involved in certain modifications of the voice, we will 

 refer more in detail to the action of different fasciculi of 

 these muscles. In this connection we will only describe 

 very briefly their situation and attachments, and the general 

 results of their contraction. 



The thyro-arytenoid muscles are situated within the 

 larynx. They are broad and flat, and arise in front from 

 the upper part of the crico-thyroid membrane and the lower 

 half of the thyroid cartilage. From this line of origin, each 

 muscle passes backward in two fasciculi, both of which are 

 attached to the anterior surface and outer border of the 

 arytenoid cartilages. The application of galvanism to the 

 nervous filaments distributed to these muscles has the effect 



1 A very interesting case of aphonia, reported by Dr. Knight, of Boston, in 

 which the appearances were carefully studied with the laryngoscope, seems to 

 show that the arytenoid muscle is not capable of producing any considerable 

 amount of movement, in totality, of the arytenoid cartilages. (KNIGHT, Two 

 Cases of Paralysis of Intrinsic Muscles of the Larynx. Boston Medical and Sur- 

 gical Journal, 1869, New Series, vol. in., p. 49, et seq.) 



2 LONGET, loc. tit. 



