THE LARGE INTESTINE OF THE PIG 491 



side of the small intestine. In fact the arrangement shown in 

 figure 8 might well suggest to a student of human embryology a 

 large intestine surrounding coils of small intestine. Where the 

 crossing takes place, the proximal and distal portions of the colon 

 become adherent to one another and thus the basal ends of the 

 ascending and descending portions of the future spiral become 

 fixed. It is therefore from this basal portion outward that the 

 future spiral is to be established, clearly necessitating a re- 

 arrangement of the irregular coils existing in the 70 mm. stage. 



From the stages which have now been considered, it is evident 

 that the method of development in the sheep described by Mar- 

 tin and accepted by Bonnet is not applicable to the pig. The 

 colon does not present a simple primary loop, but shows many 

 convolutions. It is true that among these the first or basal 

 loop has a definite bend or apex as seen in figures 5 to 8, but 

 this, unlike the apex in Martin's primary loop, does not become 

 the apex of the spiral in the adult. If it did so, the proximal 

 tenth of the colon in the 50-mm. pig must produce the proxi- 

 mal half of the adult spiral, and the distal nine-tenths would 

 produce only the distal half; but there is no evidence of such 

 unequal growth. It is therefore reasonable to suppose that 

 the proximal half in the embryo, which has been heavily stippled, 

 will produce a correspojiding proportion in the adult. Accord- 

 ingly the future apex may be approximately located at the transi- 

 tion between the dark and hght stippling, at a point' which in 

 these stages has not been definitely established. 



The continued advance of the spiral arrangement of the outer 

 coil is clearly shown in figures 9 and 10 (embryos of 90 and 95 

 mm. respectively). No further torsion of the colon than that 

 already recorded has taken place, but the winding up of the 

 outer basal coil has advanced from | a revolution in figure 8, 

 through 1 revolution in figure 9, to 2 complete revolutions in 

 figure 10. The way in which the bends of earher stages are 

 obliterated in this process is suggested in figure 9, where several 

 are evidently about to be taken up in a well-rounded curve. 

 The first of these, at a, has nearly disappeared. It occurs at 

 a point 2% of the distance from the ileo-colic junction to the 



