NO. II DIGESTIVE CANAL OF AMERICAN ALLIGATOR REESE IQ 



the duodeinim that, in the sections, is seen to he directly ventrad to 

 the gizzard, in the reconstruction is shown too much to the side of 

 the latter organ. The descending loops of the duodenum are cut in 

 such a way that the surrounding mesohlast forms a continuous mass 

 of tissue. 



Figure Jy represents a section through the plane 901 of figure 7. 

 The section passes through the kidneys, k, the edge of one posterior 

 appendage, pa, the large intestine, xl, and two regions of the small 

 intestine, i. 



The large intestine is here a thick walled, cylindrical structure, \l, 

 hanging from a thin mesentery, ms, in the much reduced body cavity. 

 The layers of its wall are much more fully differentiated than in the 

 more anterior regions of the enteron. The epithelium is here strati- 

 fied instead of simple columnar, and the folds into which it is 

 thrown are broader and less numerous than in the duodenum above 

 described. 



Ventrad to the large intestine, and almost in contact with it, is 

 seen the allantois, al, whose general outline was noted in connection 

 with figure 7. It is an irregular structure, consisting of a very thin 

 outer layer of mesoderm, lined with a single layer of flattened 

 epithelial cells. 



Lying at a considerable distance ventrad to the main body of the 

 section, are seen the two sections of the small intestine, %, surrounded 

 by irregular strands of tissue from the umbilicus. The structure of 

 these two intestinal loops is about the same as in the more anterior 

 region described above. 



Figure 7G, the last of this series, represents a section through the 

 cloaca, caudad to the urinary openings, in the plane 1060 of figure 7. 

 The epithelium of the cloaca is, of course, simply a continuation of 

 that of the surface of the body, somewhat thickened, perhaps, in the 

 deeper regions. 



The intromittent organ, \o, which projects cephalad from the wall 

 of the cloaca, is here seen as a three-pointed body of considerable 

 size, projecting ventrally from the body. 



Figure 8 shows in outline the enteron, from the ventral aspect, of 

 an embryo of 20 cm. total length, or at about the time of hatching. 

 The drawing was made from a dissection and, for the sake of 

 simplicity, only the enteron, respiratory organs, heart, and thymus 

 are shown. The jaw is cut through on the left side and is turned 

 over to the right, thus bringing into view the roof of the mouth, m, 

 and the dorsal side of the tongue, tn. At the same time the pharynx, 

 ph, and the wide anterior end of the oesophagus, oe, are cut open, 

 exposing the glottis, gs, and vocal cords, vc. 



