INTESTINAL TRACT OF BIKDS. 175 



this memoir represent the intestinal tracts of various birds as seen in preparations of 

 the kind described, and therefore illustrate the morphological conditions of the tracts. 

 In 1896 (26) I had already a considerable material, and described and figured some of 

 the chief modifications of the common type displayed in the groups of birds. Since 

 then I have been able to add largely to my material. I have now examined many 

 hundreds of birds, including a number of rare forms, and representing nearly all the 

 important groups of birds. Taking the System given by Dr. Gadow in Bronn's ' Thier- 

 Beich,' vol. vi. part ii. pp. 299-301, as one specially familiar to anatomists, I find that my 

 material includes, so far of course as living forms go, all the groups of B/atites, and, of 

 Carinates, all the Orders, all the Suborders except Mesites, and all the Families except 

 MesitidaB, Galbulidse, and some Passerine families. For materials I am indebted to the 

 authorities of the National Collection, who have allowed me to examine a number of 

 spirit-specimens, to several private persons, including in particular Mr. C. Hose of 

 Borneo through Mi\ Beddard, but above all to the Zoological Society of London. 

 Nearly all the work was done at the Prosector! um on materials from the Gardens or 

 sent to the Prosector. To my friend the Prosector, Mr. Beddard, F.R.S., I am deeply 

 indebted both for materials and assistance. To Prof. Howes, F.R.S., I am indebted for 

 many valuable references to literature, and I have had the- advantage of discussing the 

 nomenclature of characters with Prof. Ray Lankester, F.K..S. 



THE TRACT IN PALAMKDEA COBNUTA AS AN ARCHECENTRIC TYPE. 



It is convenient to describe the conditions of the intestinal tract in one form in some 

 detail so as to provide a standard for comparison and to avoid unnecessary repetition. 

 In a former paper (26. p. 138, fig. 2) I took the condition in an embryo of an Argus 

 Pheasant, about thirty days old, as a starting-point ; here, for various reasons which will 

 appear later, I begin with the condition in the Horned Screamer, Palamedea cornuta 

 (fig. 1). When unfolded, in the fashion already described, the intestinal tract is seen 

 to present three main portions between the pyloric cut end (p.) and the cloacal cut 

 extremity (cl.}. The first division from^. to the point where, at p.v., the cut portal vein 

 is represented consists of a long, narrow, and closed loop ; this is the duodenal loop of 

 Cuvier : it contains the pancreas between its ascending and descending limbs, and 

 receives the ducts of the pancreas and liver. It always in the undisturbed condition 

 lies bent backwards towards the cloaca, ventrad of all the other loops, and is therefore 

 the first portion of the gut to be seen when the abdomen is opened from the ventral 

 surface in the usual fashion. Its ascending and descending limbs are held together by 

 a narrow outgrowth of the mesentery. The mesentery, after leaving the duodenum, 

 expands into a large, nearly circular fold, at the circumference of which, from the 

 end of the duodenum to c.c., the point of insertion of the caeca, is suspended the great 

 portion of the intestine. About the middle of this portion is situated Meckel's Diverti- 

 culum (m.\ which is well known to be a relic of the embryonic stalk of the yolk-sac 

 (cf. 26. fig. 2). This portion I name Meckel's Tract, as it carries Meckel's diverticulum. 

 In Palamedea it presents a number of minor, simple corrugations, but in more specialized 

 forms the loops present extremely definite and well-marked types of divergence from 



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