On the Anatomy of Antechinomys and some other Marsupials, with special reference to the Intestinal Tract and Mesenteries of these and other Mammals
Authors: Beddard Frank E. 
Published: August 2010

Resumé.

I extract from the foregoing pages the principal new facts which I have been able to add to our knowledge of the intestinal tract of mammals and to certain features in the anatomy of the Marsupialia.

 The most important features in the visceral anatomy of Antechinomys are: the intestine borne upon a continuous mesentery, the absence of a Spigelian lobe in the liver, the wide dilatation of the uteri at their junction with the Fallopian tube, the development of a short unpaired cæcal chamber at the junction of the uteri.

 A specimen of Phascologale macdonellensis showed a persistent umbilical membrane (proving an umbilical placentation in this species), which passes between the fibres of the rectus muscle divided for its passage, and is continuous with the great and splenic omentum. The umbilical membrane is also attached to small intestine. The intestinal canal is short and carried on a continuous mesentery. The liver in this species, as in P. penicillata, has a Spigelian lobe, also present in the genus Sminthopsis.

 In many (? in all) Marsupials the suprarenal bodies receive a vein from the parietes as well as emit one to the renal vein or postcaval as the case may be; there is thus a rudiment of a suprarenal portal system in these animals, not found in at least many Eutherian Mammals.

 Though the intestinal tract, of Marsupials is on the whole simple, there are traces (Didelphys, Trichosurus) of the ansæ coli and (Trichosurus) of the colico‐duodenal ligament of more differentiated forms.

 A gut suspended upon a continuous mesentery is described for the fist time not only in Antechinomys, but in Tamandua; on the other band, a number of genera of Carnivora are described and the alleged continuous mesentery in Ursus is shown to be only apparent and due to the reduction of the ligamentum cavoduodenale. The continuous mesentery of Centetes is shown to be not universal in the species and is therefore probably to be looked upon as a reversion.

 To the numerous descriptions and figures of Rodents' alimentary tracts gathered together or published for the first time by Tullberg, a description of the colon and ansaæ coli of Otomys, Aulacodus, and some other forms is added. The enormously long ansa coli dextra of the latter shows that the spiral found in certain Rodents is not necessarily to be looked upon a4 due to the need for packing away such a long loop. The spiral of Hydrochœrus is shown to be a late development since it does not occur in half‐grown examples. The colon of the minute Arvicanthis (with one ansa only, the a. paracæcalis) shows that in this group reduction of size is not necessarily accompanied by entire simplification of the gut.

 The older descriptions of the spiral coil in certain Lemurs, e.g. Nycticebus, are shown to be correct as against more recent statements. Microcebus is shown to possess a simple colon without ansæ. Galago (2 spp.) is shown to possess a spiral like Nycticebus &c. And it is pointed out that all the forms with a specialised gut, i. e. with this spiral, are also specialised in the loss of the elsewhere characteristic carpal vibrissæ.

 Some account is given of the alimentary tract of the little known species Theropithecus gelada and Semnopithecus melalophus and the American Chrysothrix sciureus.

 The intestinal tract of Hyrax, contrary to some statements, has been shown to possess an ansa paracæcalis which may perhaps be compared to that of the Perissodactyla, and to possess the ligamentum colico‐duodenale of more differentiated forms.

 As a very general rule the loops of the small intestine are loose folds not in any way fixed. Rarely, however (e. g. Dasypus vellerosus), I have found them to be fixed.

 That the colic loops vary is shown by the instance of Lagostomus trichodactylus, in which each of the three individuals dissected by myself or Tullberg is slightly different in the proportions of those loops, and by Hyrax capenuis.

 It has been pointed out that in man the omentum is at first attached to the right side of the transverse colon and subsequently to the left side, the intermediate space being filled up later. The two earlier stages are represented in lower mammals; in Trichosurus the omentum is attached to the colon only on the extreme right of the transverse bend, and in Orycteropus and Hyrax the attachment is double, to the early part of the colon and to a more distal region—the intervening tract being free of the omentum.

 The view, deducible from previous investigations, that four stages of advancing complexity are shown in the Mammalian gut, is strengthened by fresh facts; the Lemurs are shown to be the only group in which all but one of these four stages occur.