154 



DISSECTION OF THE LARYNX. 



Fig. 41. ascend somewhat, and are inserted in- 



to the upper part of the outer surface 

 of the arytaenoid cartilage, and blend 

 with the depressor of the epiglottis. 

 The internal and lower fibres, 8 , are 

 transverse, and form a thick bundle, 

 which is inserted into the fore part of 

 the base of that cartilage, and into the 

 outer surface. 



By its outer surface the muscle is in 

 contact with the thyroid cartilage ; and 

 the inner surface rests on the vocal 

 cords, and on the ventricle of the 

 larynx and the pouch. 



Action. It moves forwards the ary- 

 trenoid cartilage towards the thyroid, 

 and relaxes the vocal cord. By a thin 

 band of fibres along the upper edge the 

 rima glottidis can be narrowed, and the 

 cord put into the vocalizing position. 



The DEPRESSOR OF THE EPIGLOT- 

 TIS (fig. 41, 5 ) (thyro-arytaeno-epiglot- 

 tideus) is a thin muscular layer by the 

 side of the upper opening of the larynx. 

 Its fibres arise posteriorly from the 

 front of the arytsenoid cartilage, some 

 being continuous below with fibres of 

 the arytrcnoid and thyro-arytrenoid 

 muscles ; and anteriorly by a narrow 

 slip from the thyroid cartilage near the 

 middle line. From those attachments 

 the fibres turn upwards with very dif- 

 ferent directions, and are inserted into 

 the border of the epiglottis on the same 

 side. The strength of the muscle va- 

 ries much in different bodies. 



Some of the lower fibres of the 

 muscle, which cover the top of the 

 laryngeal pouch, have been described by Mr. Hilton as a separate muscle 

 with the name arytceno-epiglottideus inferior. 



Action. By the contraction of the fibres, the tip of the arytrenoid car- 

 tilage will be moved forwards and inwards, and the eppiglottis will be 

 lowered over the orifice of the larynx. 



The fibres of the muscle which are spread over the sacculus will compress 

 it, and assist in the expulsion of the contents. 



PARTS INSIDE THE LARYNX. The parts more immediately concerned 

 in the production of the voice are, the vocal cords, the glottis, and the 

 ventricle of the larynx and its pouch : these are placed within, and are 

 protected by the laryngeal cartilages. 



Dissection. For the purpose of displaying the vocal apparatus, let the 

 tube of the larynx be divided along the posterior part, as in fig. 42 ; and 

 in cutting through the arytrenoid muscle, let the incision be rather to the 

 right of the middle line, so as to avoid the nerves entering it. 



On looking into the larynx a hollow (ventricle) will .appear on each 



VIEW OF THE INTERNAL MDSCI.ES OF THE 

 LARYNX. 



1. Crico-thyroidens detached. 



2. Crico-aryuenoideiis poaticus. 



3. Crico arytsenoideus lateralis. 



4. Thyro-arytseuoidfius, superficial part. 



5. Depressor of the epiglottis. 



6. Thyro-hyoiileus, cut. 



8. Deep or transverse part of thyro-arytse- 

 noideus. 



