THE LARGE INTESTINE OF THE PIG 495 



versed so as to accompany the outer in its abnormal course. 

 Since six cases of partial or complete reversal were found in one 

 hundred embryos and none among one hundred adults, the ques- 

 tion arises whether the condition may be ultimately corrected, 

 or whether like a volvulus, it may lead to fatal results. But 

 the number of specimens examined is perhaps too small to be 

 significant in this respect. 



SUMMARY 



In a series of drawings which largely explain themselves, an 

 attempt has been made to present the development of the colon 

 in the pig in greater detail than heretofore. 



The torsion of the primary intestinal loop, which in man stops 

 at 180*^, proceeds to a complete revolution in the pig; in this it 

 corresponds with the development in the sheep as described by 

 Martin. 



But the spiral coil in the pig does not begin as a single loop 

 of the colon which simply winds up, as in the sheep, according 

 to Martin and Bonnet. On the contrary it arises as a knot of 

 kinks and coils. The first of these forms the basal portion of 

 the outer limb of the permanent spiral. 



Within the limits of the colon there then appears a rotation 

 or torsion, so that the proximal part crosses the distal part, and 

 the basal coil encircles the other convolutions in the way that 

 the human colon encircles the small intestine. 



The basal coil advances by taking up secondary flexures in 

 its path until it makes two revolutions. By that time the apex 

 of the coil is about midway in the course of the spiral part of the 

 colon, and further growth of the spiral is chiefly by the coiling 

 of the apex. In estabhshing the characteristic apical pattern, 

 however, the apex advances half a turn further along the inner 

 or descending limb of the coil. 



In case the basal loop is turned in the wrong direction, or if 

 having started normally it encounters bends which do not yield, 

 complete or partial reversals of the spiral occur, six cases of 

 which Y\'ere found in embryos. 



