DEVELOPMENT OF THE HUMAN LARYNX 29 



In considering the musculature of the larynx, it soon became 

 evident, after dissections and studies of the adult larynx, that 

 there was by no means unanimity of opinion among different 

 authorities as to just what constituted the muscles of the larynx. 

 Of course, every one recognized and mentioned the cricothyreoid- 

 eus, the cricoarytaenoideus posterior and the cricoarytaenoideus 

 lateralis. But some spoke of an inter artyaenoideus muscle, others 

 divided this into an arytaenoideus transversus and artyaenoideus 

 obliquus. Some added an aryepiglotticus and a thyreoepiglotti- 

 cus ; others merely pictured one of these, and some, neither of them. 

 Others again, divide the thyreo-arytaenoid into an internus and 

 externus, and Sewell Seymour ('05) has dissected a 'small or super- 

 ficial thyreo-arytaenoid muscle' which, moreover, he differen- 

 tiates into four tj^pes. It is therefore apparent that there is not 

 yet a clear cut conception of the exact musculature of the normal 

 adult larynx. Certainly, if such difficulties present themselves 

 in the adult fully formed larynx, how much more confusion would 

 there be in attempting to isolate these varieties in a human embryo. 

 So that I arbitrarily selected the following nomenclature for the 

 laryngeal musculature, as being the simplest and most reliable: 



M. m. cricothyreoideus, cricoarytaenoideus posterior, cricoarj-- 

 taenoideus lateralis, thyreoartyaenoideus, interarytaenoideus, 

 aryepiglotticus, and thyreoepiglotticus. I have purposely regarded 

 the thyreoarytaenoideus as a single muscle, because any demar- 

 cation between an externus and internus and a small or superficial, 

 though interesting, is quite artificial, not conclusively demon- 

 strated, and not warranted by the existence of separate dis- 

 tinct action of such subdivisions. The advantage of this classi- 

 fication has been borne out by the following embryological stud- 

 ies, where each of the above enumerated muscles has been clearly 

 found, and none of the other varieties has been represented, though 

 carefully searched for. 



Embryo 109-10.5 mm. Transverse sections, 20 /i 



(Embryo 109 measures V. B. 10.5 mm. and N. B. 11 mm. in 

 length and is about 5 weeks old.) 



