996 



THE ORGANS OF DIGESTION 



Tlie duodenum still lias a lueso-duodciiuin, and is still entirely invested by 

 peritoneum. 



In man further changes take place, hut in mammals below man the condition 

 just described is that which rc^presents the normal arrangement. Fig. 597 may be 

 considered to represent in diagrannnatic fashion the simple intestine of a carnivo- 

 rous animal. 



In the human sulgect even development may not proceed bex'ond this point, 

 and the condition detailed may be met with in the adult as a permanent arrange- 

 ment. I have described some examples of this ( ' The Anatomy of the Intestinal 

 Canal and Peritoneum in Man,' London, 1885; and 'Lancet,' Oct. 13, 1888). In 

 these instances the whole of the small intestine, together with the caecum and the 

 ascending colon, were slung from a common mesentery, the attachment of which to 

 the posterior parietes was by a narrow neck giving passage to the superior mesen- 

 teric artery, and bounded by the duodenum and the transverse colon. In these 



Fig. 596.— Alimentary Canal of Cholcepus Hoffmaiunl 



sul)jects there was no trace of the mesentery proper as it is found in the normal 

 human body. The duodenum had been deprived of its meso-duodenum, and the 

 descending meso-colon was comparatively scanty; but, with these and some minor 

 exceptions, the resemblance of the arrangement of the bowels to that met with in 

 the lower animals was very exact. It is the existence of this inmiature condition 

 that predisposes to certain forms of twist or volvulus of the bowel. 



The progress of this rudimentary revolution of the intestinal tube may be noted 

 by observing the progress of the caecum. 



That prominent diverticulum lies at first below the looj) forming the lesser 

 bowel, and then to its left side. It is at first Avithout the abdomen, and is gradu- 

 ally withdrawn in the progress of development through the rapidly closing 

 umbilical opening. 



It then lies about the middle of the belly and just below the liver. Later, it 

 passes to the right side, and then descends into the right iliac fossa. 



It may be permanently arrested at any point of its course. In the condition 

 known as the congenital umbilical hernia, the gap in the anterior abdominal 



