4i8 HEAD AND NECK 



right side of the median plane, and the detached piece must be carefully 

 removed. Three muscles are now exposed, and must be cleaned. 

 They are named from below upwards : 



1. The lateral crico-arytrenoid. 



2. The thyreo-arytrenoid. 



3. The thyreo-epiglotticus. 



Musculus Cricoarytaenoideus Lateralis. The lateral crico- 

 arytcenoid muscle is triangular in form, and smaller than the 

 posterior crico-arytaenoid (Fig. 163). It springs from the 

 upper border of the lateral part of the cricoid cartilage, ex- 

 tending to the facet on the lamina which supports the base of 

 the arytaenoid cartilage ; a few of its fibres take origin from 

 the conus elasticus also. From this attachment its fibres run 

 posteriorly and upwards, and converge to be inserted into the 

 anterior surface of the processus muscularis of the arytaenoid 

 cartilage. The superficial or lateral surface of this muscle is 

 covered by the lamina of the thyreoid cartilage and the upper 

 part of the crico-thyreoid muscle ; its deep surface is applied 

 to the conus elasticus. 



Musculus Vocalis. The musculus vocalis is a sheet of 

 muscular fibres which springs, anteriorly, from the angle of 

 union of the two laminae of the thyreoid cartilage. It runs 

 posteriorly, along the ligamentum vocale and the upper part 

 of the conus elasticus, and is inserted into the lateral surface 

 of the body and the anterior surface of the muscular process 

 of the arytaenoid cartilage. Its lower fibres blend with the 

 upper margin of the lateral crico-arytaenoid muscle and the 

 medial fibres, which run along and to a certain extent are 

 attached to the ligamentum vocale, 1 form a bundle, triangular 

 in frontal section, to which the term internal thyro-arytaenoid 

 muscle was formerly applied. The vocalis muscle protracts 

 the arytaenoid cartilage, and adducts and relaxes the vocal 

 ligaments. 



Musculus Thyreoepiglotticus. The thyreo - epiglottic 

 muscle springs from the thyreoid cartilage, immediately above 

 the musculus vocalis, with the upper border of which it is more 

 or less blended. Its fibres run posteriorly and upwards, into 

 the ary-epiglottic fold, where they blend with the ary-epiglot- 

 ticus, and they are inserted into the lateral border of the 

 lower half of the epiglottis. 



1 The fibres which are attached to the ligamentum vocale are called 

 collectively the ary-vocalis muscle. 



