DEVELOPMENT OF THE HUMAN LARYNX 31 



comes the anterior arcus, and also, though less prominently from 

 a posterior portion, of itself perhaps, originating from two slightly 

 separated posteriorly lateral portions. The lateral portions then, 

 develop by a welding of the anterior and posterior portions lateral- 

 ward. At this stage then, the ventral portion of the cricoid car- 

 tilage is appreciably advanced in development over the rest of 

 this structure. It does seem difficult to reconcile this with the 

 appearance, for instance, in the 20 mm. stage, when the ventral 

 portion still persists as condensed mesenchyma, while the lateral 

 parts have undergone considerable chondrification. 



The arytaenoid cartilages. It is doubtful whether these struc- 

 tures can be determined at this early period in development; 

 probably not. There are two faint, indefinite masses which sug- 

 gest beginning condensation, but as there is a possibility of these 

 being a part of the superior portion of the cricoid, no positive 

 assertions can be made as to their independence. 



Thyreoid cartilage. This cartilage like the cricoid, makes its 

 initial appearance at this stage. I have looked in vain for its rudi- 

 ments in earlier human embryos. There has been quite a length^'- 

 discussion, during most of the nineteenth century, in which many 

 have participated, as to whether the thryeoid cartilage develops 

 from two lateral anlages which grow around and fuse ventrally, 

 or whether there is in addition to these lateral anlages, a third one 

 a pars intermedia. Nicolas, in his excellent resume of the subject 

 treats this very fully. My observations inclined to the former 

 view, as in all the stages studied, the lateral portions depict a de- 

 cidedly more advanced stage of development; yet, I must add that 

 I have found no stage, where the lateral halves alone were present, 

 and in which there was no indication whatsoever of a ventral con- 

 densation. Fig. 2 shows the thjTCoid cartilage as it exists in a 10.5 

 mm. embryo. It will be noticed that there is no interruption in 

 the continuity between the two lateral portions via the ventral 

 part ; but it will also be seen that the lateral parts exhibit a denser 

 condensation. There is no suggestion of an inferior or superior 

 cornu. The thryeoid cartilage merely looks like a horse shoe mass 

 of condensed mesenchyma. 



