DEVELOPMENT OF THE HUMAN LARYNX 41 



THE CARTILAGES 



The thyreoid cartilage is a peculiar structure at this stage, still 

 consisting purely of condensed mesenchyma. The lateral alae are 

 united ventrally, but it is to the odd shape of the lateral masses, 

 that I would call attention. Fig. 13 shows a graphic reconstruc- 

 tion of this cartilage from the side view. The superior cornu, fig. 

 13, is in evidence, and is in correct relation to the greater cornu 

 of the hyoid bone, between which develops the thyreohyoid liga- 

 ment. Another point in favor of this being the superior cornu of 

 the thyreoid, is the attachment to it of the inferior constrictor 

 pharyngis, as seen in fig. 11. Posterior, and below them, protrudes 

 a curious cylindrical mass of condensed mesenchyma, which un- 

 doubtedly forms the rudiment of the inferior cornu of the thyre- 

 oid. It overlaps the cricoid and is in close apposition to it as 

 shown in fig. 14. Probably there is no actual articular facet at 

 this stage. Anteriorly, there is a strange projection, without 

 apparent attachment to anything ; it seems to be evidence of 

 greater activity of growth in the ventral part of this lateral mass, 

 just as the superior and inferior cornua are the results of active 

 growth in the posterior portion of this lateral mass. Apparently 

 then, the directly lateral part lags behind temporarily, and the 

 peculiar gap between the anterior cornu (as I call this odd projec- 

 tion) and the superior cornu, is filled in during the next week 

 or so. 



In the 20 mm. stage, there appears to be a slight tendency to 

 condensation in this area, not marked enough to be included in 

 the reconstruction of this stage. 



The cricoid cartilage (fig. 10) consists of pure condensed mesen- 

 chyma, with no evidence as yei of chondrification. Although 

 rather crude in outline, yet it begins to suggest roughly the ma- 

 turer form. Its relation to the thyreoid cartilage resembles the 

 adult rather closely, and the continued ring, ventral and dorsal, 

 is now complete. Also, the posterior portion is enlarging and 

 begins to show advances over the relatively slower growth of the 

 anterior arcus, conforming with the adult type. Certainly, it 

 is further advanced than the thyreoid cartilage. 



