50 H. LISSER 



THE CARTILAGES 



Thyreoid. This cartilage is easily recognized at this stage and 

 has a definite outline. Although it has not attained the adult 

 shape, in all particulars, it has, nevertheless, developed into the 

 adult type. Not all of the tissue representing this structure, is 

 composed of true cartilage, and fig. 27 gives, from a lateral aspect, 

 some conception of the relative portions of chondrification and pre- 

 cartilage. Very little, if any, of the anterior, ventral, median 

 portion, between the two wings is represented by cartilage, this 

 being almost entirely condensed mesenchyme. This is well illus- 

 trated in figs. 29 and 30, which likewise depict the broad generous 

 curve (convex throughout) uniting the two wings ventrally. The 

 notched appearance with the prominent ventral ridge is not evi- 

 dent as yet. This ventral portion, in a vertical direction (caudo- 

 cephalad) is not very extensive, being appreciably^ smaller in height 

 than in the adult (relatively). 



The wings of the thyreoid cartilage are quite well developed in- 

 deed, as can be seen in figs. 29 and 32, showing considerable chon- 

 drification. 



The upper cornu is prominent, but it does not present the up- 

 ward curve, as strikingly as in the adult. Its attachment to the 

 greater cornu of the hyoid by the thyrohyoid ligament is well 

 seen, — the latter appearing as condensed mesenchyme. Just 

 where the thyreoid leaves off, and the ligament begins, and where 

 the latter establishes connection with the hyoid, cannot be defi- 

 nitely ascertained, but the continuity of the parts is easily demon- 

 strated, by graphic reconstruction, as shown in fig. 28. 



The inferior cornu of the thryeoid is of a more exaggerated type 

 than in the adult, projecting from the wings over the lateral pos- 

 terior portion of the cricoid. The relations of these two cartilages 

 are shown in fig. 28. A study, in cross sections, of these two 

 cartilages reveals an ummistakable apposition — not approximate, 

 but in close contact. Whether there is an actual articular facet 

 present at this stage, is difficult to determine. The wax model 

 suggests such a possibility very strongly but the appearance is with- 

 in the limits of error, unavoidable in the construction of such a 



