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other. Now, the parallel position of the cords to a column of 

 air ascending through the trachea admits of being restored by 

 a rotation inwards of the arytenoid cartilages on their horizon- 

 tal axes, which motion will cause the outer spur of the arytenoid 

 to describe an arc of a circle in a direction upwards, and the 

 apex to describe a similar motion in a direction inwards. We 

 shall now proceed to examine the apparatus which we con- 

 ceive to be capable of effecting this movement. 



*' The concave posterior surfaces of the arytenoid car- 

 tilages are occupied in the recent state by a muscle called the 

 arytenoid ; the fibres of this muscle pass transversely from the 

 outer edge of one cartilage to a similar position on the oppo- 

 site, and the action of the muscle is to approximate the pos- 

 terior internal margins of the arytenoid cartilages, and to se- 

 parate the anterior spurs ; or, in other words, to rotate the 

 arytenoid cartilages on their vertical axes in a direction out- 

 wards. But, in addition to these fibres, there are others which 

 are usually denominated the oblique arytenoid muscles ; it is 

 to these latter that I wish to direct yoicr especial attention. 

 The arrangement of these muscular bands is as follows : — one 

 set of fibres passes from the apex of the right cartilage to the 

 extreme outer angle of the base of the left, and another band 

 of fibres passes in a similar manner from the apex of the left 

 to the base of the right ; the two bands of fibres forming a cru- 

 cial intersection on the posterior surfaces of the arytenoid 

 cartilages. The oblique arytenoid muscles, being thrown into 

 action, produce a rotation of the arytenoid cartilages on their 

 horizontal axes ; their apices are drawn inwards and approx- 

 imated, while the outer margin of the base of each is at the 

 same time elevated, and the anterior spurs consequently un- 

 dergo a rotation inwards : the vocal cords are thus brought into 

 the desired state of parallelism, and so, by this simple ar- 

 rangement, the conditions necessary for the production of a 

 sonorous vibration arc fulfilled. 



" It should be observed, however, that although the ob- 



