THE CRITICAL PERIOD IN THE DEVELOPMENT 

 OF THE INTESTINES 



C. R. BARDEEN 



From the Anatomical Laboratory, University of Wisconsin 



ELEVEN FIGURES (FOUR PLATES) 



In studying the variations of structure found in any part of the 

 body it is of importance to distinguish the less variable from the 

 more variable features. As a rule, the less variable features are 

 associated with fundamental processes occurring early in onto- 

 genetic development, the more variable features with processes 

 of growth and differentiation occurring later in ontogenetic de- 

 velopment. Thus while it is comparatively rare to have varia- 

 tion in the number of the digits, finger prints are specific for each 

 individual. 



In the development of the human intestines three fundamental 

 loops are formed. First, the entero-colic which extends forward 

 into the umbilical cord and is supplied by the superior mesenteric 

 artery. Second, the gastro-duodenal, which projects to the right 

 at the base of the entero-colic loop and is supplied chiefly by a 

 branch of the coeliac artery. Third, the left colic which projects 

 to the left at the base of the entero-colic loop and is supplied 

 chiefly by the inferior mesenteric artery. 



The entero-colic loop undergoes normally an elaborate develop- 

 ment and gives rise to the distal part of the duodenum, the jeju- 

 num, ileum, caecum, ascending colon and the right half of the 

 transverse colon. The center of the base of the mesentery of this 

 loop is in the region of the origin of the omphalo-mesenteric or 

 superior mesenteric artery from the aorta. This becomes frxed 

 at an early period opposite the first lumbar vertebra and seldom 

 varies in position. The loop itself shows frequent variations in 

 development, some of a fundamental character, others slight. 

 These will be discussed below. 



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