190 JAY ARTHUR MYERS 



mesenchyma referred to is continuous with, and seems to have mi- 

 grated inward from, that occupying the space between the carti- 

 lages. The same condition exists between the tube and all the 

 cartilaginous elements in the region of the tracheal bifurcation in a 

 296 horn- embryo. In a 332 hour embryo these intervening mesen- 

 chymal cells possess numerous protoplasmic processes which form a 

 loose network and which, at the 356 hour stage, become smaller and 

 resemble short connective tissue fibers. In these spaces between 

 the developing cartilages and the epithelial tube small, but dis- 

 tinct, fibers appear in a 404 hour embryo. These are true connec- 

 tive tissue fibers since they stand out very prominently when 

 treated with Mallory's connective tissue stain. At this stage, 

 the tissue now forms a loose connection between the epithelium 

 on the one hand and the cartilage and intercartilaginous struc- 

 tures on the other. It contains blood vessels and nerves and con- 

 stitutes the submucosa. As in the adult, there is no sharp line 

 of demarcation between the submucosa and the tunica propria. 



4- Musculature 



In the 164 hour embryo areas of differentiated cells may be 

 observed between the ribs. Similar aggregates of cells extend 

 from the antero-lateral process of the sternum to the trachea, 

 somewhat above its bifurcation. The cells composing these ag- 

 gregates have large oval nuclei, each of which possesses a dis- 

 tinct nucleolus ; and their cytoplasm, which has a strong affinity for 

 eosin, appears to be drawn out into short strands. These struc- 

 tures are more prominent in a 176 hour embryo. Wunderlich 

 states that the muscular system begins to differentiate on the 

 tenth day in Fringilla domestica and on the twelfth day in Anas 

 boschas. 



In the 188 horn- stage numerous cytoplasmic strands have 

 united to form long bundles which consist of minute fibrils. 

 These bundles are present throughout the entire extent of the 

 developing muscles, from the sternum to the cephalic end of 

 the trachea. The nuclei are oval and several seem to belong to 

 each bundle of fibrils. At the point where these bundles, or the 



