THE SYRINX OF GALLUS DOMESTICUS 189 



parts. These cartilages often appear fused into a single mass 

 for at least a part of their extent. 



In a 452 hour embrj^o, the last of the series, most of the tra- 

 cheal rings cephalad to the tenth present two prolongations of 

 precartilage, one of which is directed cephalad, the other caudad. 

 The second to the tenth rings, inclusive, are now more or less 

 perfect squares when seen in cross section. The third, the fourth, 

 and the fifth, however, are much larger than the others (fig. 

 16). The first is roimd and still quite small. The intermediate 

 cartilages also present a different appearance; being somewhat 

 compressed, they now appear oblong in cross section. All of 

 these cartilages are relatively much larger in all developmental 

 stages than in the adult. 



In cross section, the shaft of the pessulus is becoming slightly 

 triangular, but it still does not possess the distinctly triangular 

 shape of that of the adult. The first bronchial half-rings are 

 only slightly compressed. At their dorsal extremities there are 

 indications of fusion with the pessulus, while at their ventral 

 extremities the two structures are separated onl}^ by their peri- 

 chondria. 



Wunderlich found the s;yTingeal skeleton of a 17 day chicken 

 embryo to be composed entirely of cartilage. He states that these 

 elements are cartilaginous in Fringilla domestica and Anas bos- 

 chas at the time of hatching. Rathke states that at hatching 

 ossification has begun in the sjTinx of the domestic chicken. In 

 this investigation, however, no bone was observed in the s\Tinx 

 of G alius domesticus at the time of hatching, nor in stages one day 

 later. 



3. Suhmucosa 



In the earlier stages, the anlagen of the skeletal elements, ex- 

 cept the pessulus, are in such close contact with the epithelial 

 tube that they produce actual evaginations of the epithelium (fig. 

 13) . In a 284 hour embryo this is not true of the third and the fourth 

 intermediate syringeal cartilages, and of the first half-rings; here, 

 even typical mesenchymal cells occupy the considerable space be- 

 tween the above structures and the epithehal tube (fig. 15). The 



