DEVELOPMENT OF THE HUMAN LARYNX 51 



model. Nicolas ('94), in his excellent studies on the thyreoid 

 cartilage, insists that the articulations crico-thyreoid and cricoary- 

 taenoid appear very late. I am inclined to disagree with him on 

 that score. Certainly the rudiments of such an articulation are 

 present, at least of the crico-thyreoid. However I would not 

 make a positive assertion as to the completeness of the articula- 

 tion, because of the possibilities of error as mentioned above. 



The cricoid (fig. 25). This structure is likewise very well de- 

 veloped at this stage, corresponding with the adult tj^Q even more 

 closely than does the thyreoid. Its seal ring appearance is quite 

 characteristic. Its shape is almost round and accordingly shows 

 a corresponding development in the larynx lumen, — for the two 

 are interrelated in their grow^th. Fig. 26 illustrates the extent of 

 chondrification in this cartilage. The ventral arcus is, however, 

 condensed mesenchyme (pre-cartilage) . It is quite definite, low 

 in front, gradually higher behind to the posterior arcus, which is 

 very large. The latter's posterior surface seems to possess already 

 the two flat fossae for the origin of the mm. crico-arytenoidei 

 posteriores. Again, there is typical overlapping of the arytaen- 

 oid cartilage over the cricoid, in its superior portion, and the typi- 

 cal apposition again strongly pictures the possibility of a definite 

 articulation. The relation of the two cartilages is seen in fig. 28. 



The arytaenoids. These cartilages are rather behind the thy- 

 reoid and cricoid in development, certainly as regards chondri- 

 fication, which has scarcely begun, as they are almost entirely 

 composed of condensed mesenchyme. Their shape approaches 

 that of the adult type — but the fovea triangularis and fovea ob- 

 longa on the ventral surface are not at all clear. There is no defi- 

 nite processus muscularis, but the presence of all the muscles in 

 characteristic position, and with characteristic attachment, indi- 

 cates no doubt the place where this process will appear. 



The cartilages of Wrisberg and Santorini, Siccording to Nicolas, 

 *'do not appear until the other cartilages have taken definite form, 

 not becoming cartilagenous until the epiglottis is fully formed at 

 6| months." The first part of the statement is rather indefinite. 

 I should say that all the other cartilages had definite form even 

 before this stage, but surely at the 20 mm. stage. Certainly, the 



