64 H, LISSER 



pendent of each other. The upper group contains the crico- 

 thyreoideus, cricoarytaenoideus lateraHs and thyrearytaenoideus. 

 The lower mass, the cricoarytaenoideus posterior is well differ- 

 entiated. The interarytaenoideus has not yet appeared nor the 

 ar^'epiglotticus nor the thyreoepiglotticus. There is apparently 

 no relation with the pharyngeal constrictors. 



2. During the following w^eek, the sixth week of embryonic 

 life (14 and 16 mm.) the cartilages though still existing purely as 

 condensed mesenchj^ma, have developed into distinctly outlined 

 masses; the arytaenoids have made their appearance during this 

 time. The muscles have grown with considerable rapidity, so 

 that by the end of the sixth week, they can be well differentiated 

 from each other; have received all their innervation, and have 

 developed abundant fibrillation. The thyreoepiglotticus and ary- 

 epiglotticus are still absent however. The nerves have advanced 

 correspondingly and can be traced to their final terminations, and 

 the anastomosis between the inferior and superior laryngeal nerves 

 has been accomplished. In comparison to the adult form, the 

 larynx at this stage gives an impression of being crowded upon 

 itself. 



3. By the end of the seventh week (?) (20 mm.) the larynx has 

 assumed its adult relationships, both externally with regard to 

 neighboring organs and internally with respect to its various con- 

 stituents. All the cartilages with the exception of those of Wris- 

 berg and Santorini are well developed. All the muscles are clearly 

 represented, capable of absolute differentiation; and the gross 

 nerve supply of the region is likewise complete. 



4. The existence of such a sphincter as Strazza describes seems 

 very doubtful indeed, as there are no clear indications of it in the 

 specimens studied, and the very first indication of the laryngeal 

 musculature shows several independent masses. 



5. Finally I desire to record my strong impression that the hu- 

 man larynx develops as a unit ; that its cartilages and muscles are 

 dependent or interrelated with the pharynx or the tongue in their 

 development, in no further degree, than is the natural association 

 of one part of the body with a contiguous portion. 



