l6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 56 



The ascending intestinal loop is of slightly less caliber than the 

 descending loop above mentioned ; it passes dorsal and cephalad to 

 the posterior border of the gizzard where its lumen is continuous, 

 for a short distance, with that of the descending loop above 

 described. This unusual condition is probably abnormal, but owing 

 to lack of material only one series of this stage was studied. 



At the dorso-caudal angle of the gizzard the small intestine, i, 

 opens into the ventral side of a larger tube which may be called the 

 large intestine, il. The blind end of the large intestine, cephalad to 

 the opening of the small intestine, projects forward, dorsal to the 

 gizzard, as a sort of caecum, ce, though this structure is generally 

 stated to be wanting in the crocodilia. and is not seen in the next 

 stage. 



From the caecum the large intestine passes in a ventro-caudal 

 direction, with gradually decreasing caliber, to the cloaca, from 

 whose anterior wall the intromittent organ, io, projects. 



From the ventral wall of the large intestine, at a point about one- 

 third the distance from the cloaca to the caecum, projects ventrad and 

 cephalad the stalk of the allantois, al. Owing to its thin walls and 

 small lumen the allantois was traced only a short distance into the 

 umbilical stalk. 



The profile of the liver, li, has, at this stage, about the same area 

 and even outline as that of the lung. It lies, of course, on both 

 sides of the enteron proper, and overlaps, anteriorly, as has been 

 said, the posterior end of the lung. 



Figure /a represents a section through the plane 305 of figure 7. 

 A considerable advance in the general development of the organs is 

 seen over the last stage studied. The spinal column is well outlined 

 in cartilage, and the ribs are cut at various places, r. In the body 

 wall a considerable differentiation of muscular tissue has taken place, 

 but it is only faintly shown in this series of figures. The scales, 

 especially along the mid-dorsal line, are shown as an area of less 

 closely dotted tissue. 



The lungs, lu, cut here through their anterior ends, are large, but 

 do not nearly fill the cavities, be, in which they lie ; they have the 

 sacculated appearance characteristic of embryonic lung tissue. 



The oesophagus, oe, is cut through about its middle region, where 

 its caliber is greatest. As was said above, its dorso-ventral diameter 

 is more than twice its lateral diameter, caused partly by the oblique 

 angle at which it was cut. Its wall, figure ya, is very thin and 

 exhibits a dense layer of mesoblastic tissue, in which circular and 

 longitudinal muscle layers are beginning to dififerentiate. It is lined 

 by an epithelium which here consists of a single layer of columnar 



