THE LARGE INTESTINE OB^ THE PIG 487 



After this rotation of 360°, the Hiiib of tlie loop which was origi- 

 nally posterior has again become posterior (as seen by compar- 

 ing figs. 1 and 4), but the anterior limb now crosses it twice. 

 As duodenum, it passes down on the right side of the colic or 

 posterior hmb, then bends to the left beneath the colon, and 

 finally passes upward crossing the colon a second time, but now 

 on its left side. Figure 3 is an interesting intermediate stage in 

 this process. The first rotation, of 180°, has been completed, 

 even to the apex of the primary loop (which is not the case in 

 figure 2), and the second rotation of 180^ has occurred in the 

 proximal part of the loop, but not distally. The rotation ex- 

 tends from the proximal portion of the loop outward, and the 

 process has been completed in the distal part of the loop in 

 figure 4. 



Martin observed a similarly complete rotation in tlie sheep and 

 described it as follows: 



The more the small intestine forms coils, the more it crowds the re- 

 current colic limb dorsally and at the same time to the right and cau- 

 dally, until it is surrounded b}^ a ring of coils of small intestines; and the 

 half axial rotation about the mesentery in a 56-day embryo is trans- 

 formed into a complete rotation. Thereby the relation of duodenum 

 to the large intestine becomes changed. Earlier only' a simple crossing 

 took place, but now there is an encircling. 



In the pig, MacCallum described the rotation in connection 

 with the various groups of coils which he recognized. Thus he 

 states that 'Group D,' which includes those coils of the small 

 intestine which are nearest the caecum, "has rotated posteriorly, 



dorsally, and to the right It thus moves pr.st 



Group C and carries the caecum with it, so that the beginning 

 of the large intestine lies dorsally and posterior to Group D." 

 Correspondingly a group of coils of the large intestine (Group 

 E) is said to "rotate through three-quarters of a circle." Al- 

 though it is apparent that the rotation was observed, its 

 description is unnecessarily involved, since it is based on 

 groups of coils of questionable distinctness, rather than on the 

 limbs of the primary looi?. 



