38 H- LISSER 



and assume a clearer outline. Figs. 4 and 5, show two sections 

 of this cartilage. These drawings of course, are of necessity, ex- 

 aggerated, as no such absolutely isolated areas exist for they fade 

 off imperceptibly into the surrounding tissue, and outlines must 

 be somewhat arbitrarily decided upon. The lumen is still narrow 

 and slit-like, so that the circular, ring-like appearance of the cri- 

 coid is not yet established. The sides seem compressed more or 

 less one upon the other. 



The artaenoid masses, (fig. 4), make their appearance at this 

 time, and although rather intimateh' related to the cricoid mass, 

 nevertheless permit of recognition. They are roughly of oval 

 shape and bear little resemblance to their adult appearance. 

 They are of course composed purely of precartilage ; they develop 

 more slowly than do the cricoid or thyreoid, but keep abreast 

 of the epiglottis in their growth. Even at the 20 mm. stage when 

 the cricoid and thyreoid show a predominance of chondrificati^n, 

 the arytaenoids and epiglottis are still represented only by con- 

 densed mesenchyma. 



The epiglottis. The epiglottis is shown in fig. 3 ; it is situated at 

 a lower level than in the adult. 



There is a crowding together of laryngeal structures at this 

 period in development. In the adult the length or height of the 

 epiglottis is much greater than its breadth while in the embryo 

 the length and breadth are about equal. This congestion of the 

 cartilage is very likely due, in great part, to the general ventral 

 curvature of the entire embryo, especially the way the head is bent 

 upon the body and with the subsequent lengthening out and 

 straightening out of the whole body, the laryngeal cartilages 

 naturally assume their adult relationship. Such changes, though 

 partial, have already occurred by the 20 mm. stage, as seen in fig. 

 38 of the model and illustrate the tendency, which is fulfilled more 

 markedly later. 



The hyoid hone and styloid process are composed of condensed 

 mesenchyma and are very clearly outlined. Fig. 3 shows this. 

 The greater cornu is developing rapidly and has attained large 

 proportions. 



