256 PHILOSOPHrCAL TRANSACTIONS. [aNNO IGQS. 



Now here is observed that remarkable difFereiice from many other animals, 

 that we cannot but make two mesenteries ; one peculiar to the small guts, the 

 other to the great ones ; and for distinction sake, I shall call the former mesen- 

 terium minorum, and the latter mesenterium majorum, sc. intestinorum. For 

 as the duodenum descended from the stomach, it ran under the colon, just 

 where it is joined to the caecum, towards the middle of the spine. Hence I 

 found a projection of the first mesentery into a spiral line, like a cochlea, or 

 winding pair of stairs; so that on inflation, these intestines made several con- 

 volutions, though not exactly spiral. The second mesentery, or mesenterium 

 majorum, was projected more in a plane, and made almost a circular figure at 

 its periphery; so that the caecum and colon almost entirely encircled the small 

 guts. 



The small guts, when inflated, measured about 6-l feet in length. The 

 caecum was about 6 inches long; and the colon and rectum 2 feet long. The 

 compass of the duodenum was 3 inches ; the ileum 2^- inches ; that of the 

 caecum, in the largest place, was 6 inches; of the colon 4 inches; and the 

 rectum was 3 inches about. From the spine to the utmost projection of the 

 small guts, under the same circumstance of inflation, measured about 6 inches ; 

 the greatest diameter that the colon in this circular figure made, was somewhat 

 above 7 inches. In the whole duct or canal of the intestines, I could not ob- 

 serve any valves, not even in the caecum itself. It is true, that the foramen 

 into the caecum was a great Jeal less than the capacity of liie gut itself; how- 

 ever, the passage into it was so open and wide, as readily to receive or emit its 

 contents. But the length, and frequent gyrations and windings, supply this 

 want of valves ; they prevent the danger of a too hasty descent of the fasces, 

 and give more opportunity for the separation of chyle into the vasa chylifera. And 

 the cochlea, or spiral figure of the first mesentery, easily prevents a regurgitation 

 of the contents of the intestines again into the stomach, on a declining posture 

 of the body of this animal, as it is frequently in, when it hangs by the tail. 

 For though the passage from the stomach by the pylorus, into the duodenum, 

 is large and open, yet in that posture of the body, there must be a reduplica- 

 tion, or folding over of the duodenum ; since the great bulk of the intestines 

 must incline towards the di,'{phragm ; by which reduplication, the passage at the 

 pylorus must, in a great measure, be obstructed ; and the ascent of the contents 

 now be as difficult and great, as when the animal stands upon its four feet. 

 The reverse of this structure of the intestines I found and have described in my 

 anatomy of the tajacu, or the Mexico musk hog : for here the colon made <i 

 spiral figure, and the small guts made a plane. In our possum the small guts 

 make a spiral, and the colon and great guts a plane. But a spiral convolution 



