180 JAY ARTHUR MYERS 



and in obtaining the curvature of the backUne of the embryo for 

 reconstructions. Most series were stained with iron or alum 

 hematoxylin, with picrofuchsin or eosin as counter stains. Some 

 of the later stages, however, were stained with Mallory's anilin- 

 blue connective tissue stain, Weigert's resorcin-fuchsin elastic 

 tissue stain, and Mayer's mucicarmine. 



In transverse sections of a 68 hour embryo, the epithelial tube 

 of the foregut is surrounded by a condensed mass of mesenchyma. 

 This tube, which in its most cephaUc part is cylindrical, when 

 followed caudad, enlarges and becomes triangular in shape. Ex- 

 tending ventrolaterally from this tube are two beginning diver- 

 ticula, the anlagen of the trachea and the bronchi. In length the 

 right is 0,05 mm. while the left is 0.03 mm. 



Embryos of 74, 78, and 80 hours show a lengthening of the 

 trachl^a and the bronchi, but the former is still relatively much 

 shorter than the latter. Wunderlich called attention to this con- 

 dition in Fringilla domestica and mentioned the fact that it rep- 

 resents a stage which is found throughout life in certain reptiles. 

 This might be regarded as a homology, but such homology is not 

 probable. It would seem that a logical explanation of this con- 

 dition might be found in a study of the position and the relations 

 of the organs of this region. Since the neck as such has not yet 

 developed it is obvious that the trachea springs from the diges- 

 tive tube and bifurcates at once at a point not far from the future 

 position of the lungs. As the neck lengthens, the oesophagus 

 and the trachea must keep pace. The trachea, therefore, becomes 

 drawn out. This elongation goes on to such an extent in the 

 chicken that the trachea eventually becomes much longer than 

 the bronchi. 



A 128 hour embryo shows a marked increase in the length of 

 the trachea and the bronchi, and in a 140 hour stage these struc- 

 tures have nearly doubled in length. The right bronchus courses 

 laterally and gives off seven sac-like branches which later become 

 the so-called pipes of the lungs. 



Since the tracheal bifurcation is the region of especial interest 

 in this paper, the general development of the trachea and the 

 bronchi will not be traced further. 



