DEVELOPMENT OF THE DIGESTIVE SYSTEM 827 



first intestinal convolution appears ; and sometimes there is a congenital 

 hernia of this kind at birth, which usually disappears under the influence 

 of gentle and continued pressure. An illustration of this is given in 

 Fig. 235. This protrusion, in the normal process of development, is 

 gradually returned into the abdomen, as the cavity of the pedicle of the 

 umbilical vesicle is obliterated, at about the tenth week. 



At the upper part of the abdominal cavity, the alimentary canal 

 presents two lateral projections, or pouches. The one on the left side, 

 as it increases in size, becomes the greater pouch of the stomach, and 

 the one on the right side, the lesser pouch (see Plate XVI, Fig. 3). 



At a short distance below the attachment of the pedicle of the 

 umbilical vesicle to the intestine, there appears a rounded diverticulum, 

 which is eventually developed into the caecum. 

 The caecum gradually recedes from the neighbor- 

 hood of the umbilicus, which is its original situa- 

 tion, and finally becomes fixed, by a shortening' 

 of the mesentery, in the right iliac region. As 

 the caecum is developed it presents a conical 

 appendage, which is at first as large as the small 

 intestine and is relatively longer than in the 

 adult. During the fourth week this appendage 

 becomes relatively smaller and more or less 

 twisted, forming the appendix vermiformis. At Fi s- 2 35- F(Ktal P& 



, . . showing a loop of intestine 



the Second month the Caecum IS at the UmblllCUS, forming- an umbilical hernia 



and the large intestine extends in a straight line ( Dalton )- 



toward the anus ; at the third month it is situated From the convexity of the 



loop, a thin filament is seen 



at about the middle of the abdomen ; and it passing to the umbilical vesi- 

 gradually descends, until it reaches the right iliac cle - wh . ich , ,1? h f ere flattened 



into a leaf-like form. 



region at about the seventh month. Thus at the 



second month, there is only a descending colon ; the transverse colon is 

 formed at the third month ; and the ascending colon, at the fifth month. 

 The ileo-caecal valve appears at the third month ; the rectum, at the 

 fourth month ; and the sigmoid flexure of the colon, at the fifth month. 

 During this time the large intestine increases more rapidly in its diame- 

 ter than the small intestine, while the latter develops more rapidly in 

 its length. 



In the early stages of development the internal surface of the intes- 

 tines is smooth ; but villi appear on its mucous membrane during the 

 latter half of intra-uterine existence. These are found at first both in the 

 large and the small intestine. At the fourth month they become shorter 

 and less abundant in the large intestine, and they are lost at about the 

 eighth month, when the projections which bound the sacculi of this 



