THE DEVELOPMENT OF THE SPIRAL COIL IN THE 

 LARGE INTESTINE OF THE PIG 



PAUL E. LINEBACK 



Harvard Medical School, Boston, Mass. 



TWENTY-THREE FIGURES 



The student of human anatomy who happens to examine the 

 viscera of the adult hog will be greatly impressed by the spiral 

 arrangement of the ascending colon. For the colon in the pig, 

 after arising from the caecum which is almost entirely on the 

 left of the mid-ventral line, passes at once to the left, and then 

 swings around the abdominal cavity in voluminous coils. The 

 small intestines are mostly hidden behind it, though they appear 

 in the right iliac fossa, and altogether the colon is the principal 

 object seen when the abdominal cavity is opened. 



To describe the course of the pig's colon in detail is a diffi- 

 cult undertaking, which John Hunter skillfully attempted in the 

 following passage {Essays and Observations, 1861) : 



It makes five spiral turns like a screw, coming nearer the center; at 

 the end of which it is bent back upon itself, passing between the former 

 turns as far as the first: but in this retrograde course it gets nearer the 

 center of the screw, so that it is entirely hid at last, then makes a 

 quick turn upward, adhering to itself and to the left kidney, as high 

 as the first spiral turn; from thence it passes across and close to the 

 spine, and before the mesentery, adhering to the lower surface of the 

 pancreas, and, as it were, encloses the fore-part of the root of the 

 mesentery; it then passes down the right side before the duodenum, 

 gets behind the bladder, and forms the rectum. 



Hunter's description was cited by Owen who notes that "the 

 spiral turns of the colon, above described, form one of the char- 

 acteristics of the Artiodactyle order." To a certain extent this 

 is true, but the cow and sheep, and doubtless other forms, pre- 

 sent considerable modifications of the arrangement found in the 



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