ALIMENTARY TRACT AND ITS APPENDAGES 



311 



bends sharply to enter the descending Hmb of the second loop. 

 This bend or duodeno-jejunal flexure (X, Fig. 179) is a relatively 

 fixed point in the growth of the intestine, and marks the bound- 

 ary between the duodenum and succeeding parts of the small 

 intestine. The second loop descends deep into the umbilical 

 cord, and the yolk-stalk is attached to its lowermost portion. 

 A bilateral swelling at the upper end of its ascending limb is the 

 primordiuni of the caecal processes, and marks the anterior end of 

 the large intestine, which passes in a slight curve to the cloaca. 

 In the subsequent growth of the intestine the fixed point 

 referred to above at the hinder end of the duodenum is held in its 

 place, and the duodenal loop in front of it simply becomes longer 



Fig. 180. — Viscera of a chick embryo of 17 days' 



incubation from the right side. (After Duval.) 



Am., Attachment of amnion to umbiHcal stalk. 

 Li. r., 1., Right and left lobes of the hver. Pc, Pan- 

 creas. U. St., Umbilical stalk. Other abbreviations 

 same as Fig. 179. 



without forming secondary convolutions; the pancreas comes to 

 lie in this loop. The second loop, on the other hand, forms 

 numerous secondary convolutions (Fig. 180) which lie at first in 

 the umbilical cord, but which are gradually retracted (seven- 

 teenth to eighteenth day) into the abdominal cavity. 



The two intestinal caeca begin to grow out as finger-shaped 

 processes from the swelling already referred to, about the seventh 

 day, and rapidly attain considerable length. The large intestine 

 elongates only about in proportion to the growth of the entire 

 embryo. 



Having thus noted the general gross anatomy of the embry- 



