28 



STRUCTURE AND CLASSIFICATION OF BIRDS 



Fig. 11. — Casuarius ; Intestinal Tract 

 (aptek Chalmeks Mitchell). 



the duodenal loop is again the only specialised region of,the 



intestine. 



The ostrich and the cassowary present but little modifi- 

 cation of the same 

 primitive type of gut. 

 In the former we have 

 a rather more com- 

 plicated duodenal loop, 

 which is furnished with 

 a small subsidiary fold. 

 Then, too, the large in- 

 testine has the same 

 remarkable folded con- 

 dition seen, but to a 

 less extent, in Chauna. 

 Casuarius is simpler 

 than Struthio. In all 

 these figures (taken 

 from Mr. Mitchell's 

 paper) the course of 

 the principal blood 

 vessels is shown ; only 

 the veins, as the arteries 

 were found invariably 

 to accompany the veins. 

 It will be observed that 

 the principal feeder of 

 the portal vein runs 

 directly across the main 

 mesenteric fold, and 

 ends near to the vitel- 

 line duct, the rudiment 

 of the yolk sac ; from 

 the junction /of this 

 with the main stem of 

 the mesenteric vein 



arise two other vessels ; one of these supplies the duodenal 



loop, the other the large intestine ; there is sometimes a 



Fig. 12.- 



-Struthio camelus; 

 Teact. 



Intestinal 



37, short-circuiting vessel cut across. (After 

 Chalmers Mitchell.) 



