434 C. R. BARDEEN 



The distribution of the branches of the superior mesenteric arterj'- 

 are, ho\vever,«suggestive. 



The branches of the superior mesenteric artery which supply 

 the free small intestines may be divided into two sets, those which 

 arise near and distal to the ileo-colic artery and those which arise 

 proximal to this artery. The former branches in the adult, in 

 the specimens I have examined, supply the distal two-thirds to 

 three-fifths of the free small intestines, the former the proximal 

 third to two-fifths. I have found the same thing true in a fetus 

 22.5 cm. long. The territory suppled by the distal branches 

 corresponds, therefore, very well with the ileum, that supplied by 

 the proximal branches, with the jejunum. The relations of the 

 two sets of branches to the mesentery and duodenum suggests 

 that the former supply the umbilical coils of the intestine, the 

 latter abdominal coils, but a definite proof of this is possible only 

 with injected specimens of early fetuses and these we unfortu- 

 nately lack. There is, however, good reason to believe that the 

 primitive umbilical coils correspoond essentially with the ileum, 

 the abdominal coils with the jejunum. If we take coils 2 and 3 

 of Mall to represent the jejunum and coils 4, 5 and 6, the ileum 

 we find from the data given by Mall (table 1 , footnotes) that the 

 ileum is about four times as long as the jejunum during the period 

 immediately preceding the return of the umbilical loop. As the 

 return of this loop takes place the abdominal coils (jejunum) 

 grow rapidly so that in the 40 mm. fetus studied by me the ratio 

 of ileum to jejunum is as 4:3. After the return of the umbilical 

 coils the ileum grows relatively much faster according to Mall's 

 data so that in a fetus 130 mm. long it is over three times as long 

 as the jejunum. In the latter part of fetal life the adult propor- 

 tions appear to be reached. 



That we are justified in assuming a primitive development of a 

 considerable part of the small intestines within the abdominal 

 cavity may, I think, be deduced from the following table showing 

 the relative development in length of the small and large intestines 

 as compared with the growth in length of the axial part of the 

 body. The data are based chiefly on those furnished bv Mall 

 ('97). 



