NO. II DIGESTIVE CANAL OF AMERICAN ALLIGATOR REESE I5 



bronchi. The caudal ends of the hmt^-s overlap the cephalic end of. 

 the liver. //. 



The oesophag-us, oc, is large, and is laterally compressed so that its 

 dorso-ventral diameter, the one shown in the present figure, is two or 

 three times as great as its .lateral diameter. This gives the impres- 

 sion, in the reconstruction, that the oesophagus is nearly as large 

 as the stomach. 



As has been said, the oesophagus does not open directly into the 

 pharynx, but is separated from it by a membrane which consists of 

 the flattened epithelial layers of both cavities separated by a thin 

 layer of mesoblast. This partition between the pharynx and the 

 oesophagus is not a mere fold of mucous membrane, but is a 

 complete, though thin, wall, easily seen in the series of sagittal 

 sections from which this region of the embryo was drawn. The 

 anterior end of the oesophagus is suddenly constricted so that the 

 actual opening closed by this partition is not large. 



Followed caudad the dorso-ventral diameter of the oesophagus 

 varies somewhat, as does the lateral diameter, but it remains large 

 throughout and opens into the stomach with no sharp line of de- 

 markation. The character of the epithelium of the enteron caudad to 

 the pharynx will be discussed in connection with the sections to be 

 described below. 



The stomach, i' , is very different in outline from wdiat was seen 

 in the last stage described, figure 6a. Instead of having approxi- 

 mately the form of the typical mammalian stomach it is now so 

 elongated that the opening into the duodenum, the pylorus, py, seems 

 to be nearer the anterior than the posterior end. While the position 

 of the pylorus is very distinct it is difficult to distinguish the line 

 of demarkation between the stomach and the oesophagus. 



The extreme caudal region of the stomach is enlarged to form a 

 blind sac, representing the gizzard, gs. A slight enlargement in the 

 region of the pylorus may represent the glandular region of the adult 

 stomach. The stomach opens, in a rather curious way, into the 

 side of the duodenum, d, the anterior end of the latter structure 

 having the appearance of a sort of caecum, to be seen in the next 

 stage of development. 



The duodenum, d, makes a U-shaped bend at the side of the 

 stomach, and then, in the region of the caudal edge of the g-izzard, 

 gz, dips suddenly ventrad and caudad towards the umbilical cord, u, 

 where it apparently ends blindly, though this appearance is probably 

 due to an artifact in the embryo from which the reconstruction was 

 made. It is likely that, in removing the embryo from the yolk, the 

 connection between the two loops, i, of the intestine was broken. 



