NO. II DIGESTIVE CANAL OF AMERICAN ALLIGATOR — REESE 7 



the thyroid gland, tg. it now lies deep in the tissue of the floor of 

 the pharynx, entirely separated from the pharyngeal epithelium. It 

 consists of a compact mass of cells, now showing a bilobed structure 

 in its anterior end, and extending through about twenty-five ten- 

 micron sections. It is solid throughout most of its extent, but. in 

 the section figured, which is near the anterior end, the lobe on the 

 right side shows a small but distinct cavity scarcely visible in the 

 figure. 



Caudad to the region just described the pharynx contracts sud- 

 denly to form the oesophagus, a narrow, V-shaped slit, which soon 

 divides into an upper and a lower cylindrical tube, figure 5D, ent. 

 Followed caudad the lower of these tubes divides into the two 

 bronchial rudiments, figure 5E, //;, which, in the embryo here figured, 

 extend through nearly one hundred sections. In the region shown 

 in figure 5E the three tubes, oe and lu, lie at the angles of an 

 imaginary equilateral triangle, while in the region of the liver, where 

 the bronchial rudiments end, the tubes lie in the same horizontal 

 plane. 



A short distance caudad to the ends of the bronchial rudiments the 

 oesophagus turns suddenly ventrad and becomes much enlarged to 

 form the stomach, figure 5F, i', which may be traced through twenty- 

 five or thirty sections in this series. The epithelium of the stomach 

 is fairly thick, and consists of five or six layers of compact, indis- 

 tinctlv outlined cells with spherical nuclei. Ventrad to the stomach 

 is seen, in figure 5F, a section of the duodenum, i, which extends, 

 with gradually diminishing caliber, for twenty-five or thirty sections 

 caudad to the posterior limit of the stomach, where it opens to the 

 yolk-sac and is lost. 



The section that cut this embryo in the posterior region of the 

 stomach also passed through the hindgut in the region of the poster- 

 ior appendages, figure 5G. There the intestine, i, is a distinct, 

 cylindrical tube which extends, with not much variation in caliber, 

 and with little variation in position, from this point to the cloaca. 

 Followed cephalad, towards the posterior intestinal portal, it grad- 

 ually diminishes in caliber, as did the foregut on approaching the 

 anterior intestinal portal. The epithelium consists here of three or 

 four layers of compactly arranged cells, and has about the same 

 appearance as in the oesophagus and duodenum. 



Figure 5H represents a section through the cloacal region, cl, 

 showing the openings into the cloaca of the Wolffian ducts, zudo. 

 Just anterior to these openings the cloaca opens ventrally into a small, 

 anteriorly-projecting pouch, the rudiment of the allantois. 



Caudad to the openings of the Wolffian ducts the cloaca extends 



