646 



DEVELOPMENT OF THE ALIMENTARY CANAL 



Fig. 242. 



umbilicus ; but between the fourth and fifth months (Cruveilhier) 

 their position is altered, and they then become fixed in the right 

 iliac region. During the first six months, the internal surface of 

 the small intestine is smooth. At the seventh month, according to 

 Cruveilhier, the valvulae conniventes begin to appear, after which 

 they increase in size till birth. The division of the colon into 

 sacculi by longitudinal and transverse bands, is also an appearance 

 which presents itself only during the last half of foetal life. Pre- 

 vious to that time, the colon is smooth and cylindrical in figure, 

 like the small intestine. 



After the small intestine is once formed, it increases very rapidly 

 in length. It grows, indeed, at this time, faster than the walls of 



the abdomen; so that it can no longer 

 be contained in the abdominal cavity, 

 but protrudes, under the form of an in- 

 testinal loop, or hernia, from the umbili- 

 cal opening. (Fig. 242.) In the human 

 embryo, this protrusion of the intestine 

 can be readily seen during the latter part 

 of the second month. At a subsequent 

 period, however, the walls of the abdo- 

 men grow more rapidly than the intes- 

 tine. They accordingly gradually en- 

 velop the hernial protrusion, and at last 

 inclose it again in the cavity of the ab- 

 domen. 



Owing to an imperfect development 

 of the abdominal walls, and an imperfect 

 closure of the umbilicus, this intestinal 



protrusion, which is normal during the early stages of foetal life, 

 sometimes remains at birth, and we then have ^congenital umbilical 

 hernia. As the parts at that time, however, have a natural tendency 

 to cicatrize and unite with each other, simple pressure is generally 

 effectual, in such cases, in retaining the hernia within the abdomen, 

 and in producing at last a complete cure. 



Urinary Bladder, Urethra, &c. It will be recollected that very 

 soon after the formation of the intestine, a vascular outgrowth takes 

 place from its posterior portion, which gradually protrudes from the 

 open walls of the abdomen in front, until it comes in contact with 

 the external investing membrane of the egg, and forms, by its con- 

 tinued growth and expansion, the allantois. (Fig. 241, /.) It is at 



FOETAL Pro, showing loop 

 of intestine, forming umbilical 

 hernia ; from a specimen iu the 

 author's possession. From the 

 convexity of the loop a thin filament 

 is seen passing to the umbilical 

 vesicle, which is here flattened into 

 a leaf-like form. 



