DEVELOPMENT OF THE HUMAN LARYNX 63 



of the various laryngeal structures, when cut in a different plane, 

 would shed further light on some of the more doubtful features. 



The cartilages are developed to practically the same extent as 

 in Embrj^o 22 (20 mm.) and an idea of their appearance in frontal 

 section, can be obtained by reference to figs. 21, 22, 23. There 

 are no differences in the cartilagenous growth of sufficient impor- 

 tance to warrant a detailed description. The high degree of chon- 

 drification can be noticed in figs. 21, 22, 23. 



The nerves likewise offer no difficulty for study, and can be 

 followed to their respective terminations. For further details 

 reference is made to the results obtained from a study of Embryo 

 22 (20 mm.). 



A word might be said about the muscles, since the cutting into 

 frontal sections presents at least this feature of interest. The 

 conception of the laryngeal musculature as a sphincter laryngeus, 

 as Strazza expressed it; with a definite horizontal direction to its 

 fibers, expecially emphasized by Kanthack, is not borne out at all 

 by a study of this embryo. The muscles like the cricoarytaenoid- 

 eus lateralis and thyreoarytaenoideus have a frontal direction to 

 their fibers, as seen in fig. 21 and 22 and by no means any hori- 

 zontal trend. Moreover the muscles are all clearly differentiated, 

 as much so as they are in the adult, and give no indication 

 whatsoever of being related or connected with the pharj^ngeal 

 constrictors. 



CONCLUSIONS 



1. Towards the end of the fifth week (?) (10.5 mm.) of embry- 

 onic life, the integral structures of the larynx, under which I in- 

 clude the precartilage masses and the premuscles masses, first 

 make their appearance. The laryngeal nerves can be recognized 

 but have not yet entered the interior of the larynx, although the 

 recurrent laryngeal has pushed upward as far as the lower portion 

 of the cricoarytaenoideus muscle. The rudiments of the cricoid 

 and thyreoid and epiglottic cartilages can be identified. The 

 arytaenoids have not made their appearance. Four premuscles 

 masses are present, two on each side of the larynx; all are inde- 



