692 



DISSECTION OF THE LAKYNX. 



consists of 

 outer 



and inner 

 parts : 



some fibres 

 from aryte- 

 noid carti- 

 lage to vocal 

 cord : 



relations 



Thyi-c- 

 epiglotti- 

 deau 

 muscle; 



membrane. The fibres are directed backwards with different inclina- 

 tions : The external (4) ascend somewhat and are inserted into the 

 outer border of the arytenoid cartilage. The internal fibres ( 8 ) are 

 horizontal, and forma thick bundle which is inserted into the margins 



of the vocal process and the 

 lower part of the outer surface 

 of that cartilage,. whilst a few 

 of the deepest fibres of the 

 muscle pass from the outer 

 surface of the vocal process of 

 the arytenoid cartilage to l>e 

 inserted into the true vocal 

 cord. 



The outer surface of 

 muscle is covered by 



the 

 the 

 the 

 the 



FIG. 246. INTERNAL MUSCLES OF THE 

 LARYNX. 



1. Crico-thyroid detached. 



2. Posterior crico-arytenoid. 



3. Lateral crico-arytenoid. 



4. Thyro-arytenoid, superficial part. 



5. Depressor of the epiglottis, consist- 

 ing of fibres of the aryteno epiglottidean 

 muscle and others given oif from the 

 thyro-arytenoid. 



6. Thyro-hyoid, cut. 



8. Deep part of thyro-arytenoid. 



is 



thyroid cartilage ; and 

 inner surface rests on 

 vocal cords, and on the ven- 

 tricle and pouch of the larynx. 

 Action, The thyro-aryte- 

 noid draws forwards the aryte- 

 noid cartilage, and causes the 

 cricoid to move forwards and 

 downwards, thus opposing the 

 crico - thyroid muscle, and 

 slackening the vocal cords. 

 It also moves inwards the 

 fore part of the arytenoid car- 

 tilage with the true vocal cord, 

 so as to place the latter in the 

 position necessary for vocali- 

 sation. The short fibres pass- 

 ing from the arytenoid carti- 

 lage to the vocal cord will 

 tighten the fore part, and relax 

 the hinder part of the cord. 



The THYRO-EPIGLOTTIDEAN 



MUSCLE is a thin layer which 

 varies much in its develop- 

 ment in different bodies. Its 

 fibres arise from the thyroid 

 cartilage in conjunction with 



the outer part of the thyro- 

 arytenoid, and are directed upwards, covering the outer surface of 

 the saccule of the larynx, to be inserted into the margin of the 

 epiglottis and the aryteno-epiglottidean fold with the aryteno- 

 epiglottidean muscle. The whole of the muscular fibres passing 

 from the arytenoid and thyroid cartilages to the epiglottis are 

 sometimes described together as the depressor of the epiglottis. 



