92 ON THE ALIMENTARY TRACT OF CERTAIN BIRDS. 



§ Summary of Facts relating to the Intestinal 

 Coils of Birds. 



We are in a position, I think, to lay down with confidence the 

 following genei-al statements with regai-d to the intestinal tract 

 of the Class Aves. These statements are deduced from the 

 memoirs of others who have written upon this subject, as well 

 as from the facts ascertained by myself, and embody in a brief 

 form what is known upon the subject dealt with in the present 

 communication : — 



(1) There are no essential difierences between the intestinal 

 tract in Birds and in Crocodilia. The most complicated alimen- 

 tary tract in Birds can be derived through a series of stages from 

 the simple Crocodilian form. 



(2) The intestinal tract of Birds diffei's from that of Mammals 

 in that there is never in the former, as there is generally in the 

 latter, a rotation of the gut coupled with an attachment of the 

 duodenum to the colon or mesocolon by a duodenal caval ligament. 

 On the other hand, there is nearly alwa^ys in Birds an ileo- 

 duodenal ligament which serves to hold together the gut and 

 which is wanting in Mammals. Furthermore, in Mammals the 

 colon may be specialised into fixed loops, while in Birds such 

 fixed loops are found only in the small intestine. 



(3) The small intestine of Birds can, with rare exceptions, be 

 distinguished into duodenal, jejunal, and ileic regions. 



(4) The duodenal region consists of a long well-defined loop 

 (only absent in certain fruit-eating Pigeons), which is usually 

 straight, but sometimes (e. g. Milvus) shows indications of — or a 

 pronounced — spiral arrangement, as it does also in certain 

 Crocodilia,. It is wider or narrower in different groups, and the 

 enclosed pancreas extends a greater or a less way towards the 

 extremity of the loop in different birds. 



(5) The jejunal region is sometimes (e. g. Gallinaceous birds) 

 marked ofi" from the duodenal by a sudden diminiition in calibre. 

 It is usually the longest section of the gut ; but is sometimes as 

 short or even shorter than either the duodenal ot ileic region or 

 both. It may be a tract of intestine without any fixed loops (as 

 in the Gallinaceous birds, various Passerines, &c.), but if of con- 

 siderable length is usually specialised into a series of two or more 

 fixed narrow loops, which may be interconnected by secondary 

 mesenteries in different ways, distinctive of difierent groups of 

 birds. An intermediate condition is seen (e. g. among Accipitres 

 and in Fregatct), where the jejunum is not arranged in lax and 

 alterable coils as iii the Gallinaceous birds, but is stiffened here 

 and there into wide loops, which are not so sharply marked off 

 as in the more specialised birds and are not interconnected by 

 secondary mesenteries. 



(6) The ileic region is not always quite distinct from the 

 jejunal, and degrees of distinctness occur. In less specialised 

 intestines there is no definite loop, but the end of the ileum is 



