io8 



THE BIOLOGY OF BIRDS 



ST 2 



Fig. 25. — Food-canal of an eagle. 

 From a specimen. T., tongue ; 

 GL., glottis ; GU., gullet ; CR., 

 crop ; TR., cut end of trachea ; 

 ST. I, anterior part of stomach; 

 ST. 2, posterior or pyloric part of 

 stomach; d., duodenum; s.i., 

 small intestine ; c, caeca ; L.i., 

 large intestine or rectum ; CL., 

 cloaca. 



way the other loops will under- 

 go the least possible disturb- 

 ance " (Newton, 1893, p. 144). 



At the junction of the 

 ileum or small intestine with 

 the rectum or large intestine 

 there is a valve (ileo-caecal), 

 preventing a return of the 

 contents, and there are usually 

 two blind diverticula, the caeca. 

 In rare cases, e.g. herons, there 

 is only one ; in rarer cases, 

 e.g. some parrots, there is 

 none. The cseca occur in all 

 sizes, from mere vestiges, e.g. 

 in the pigeon, to long func- 

 tional tubes, as in the duck. 

 In the ostrich the caeca are 

 not only very large, but they 

 contain a spiral valve. When 

 the caeca are large enough to 

 be of use they serve as culs- 

 de-sac in which the food is 

 delayed in its downward pas- 

 sage. " It is probable that in 

 them certain hitherto undis- 

 solved matter, as cellulose and 

 possibly chitin, is acted upon 

 by marsh-gas, so as to extract 

 as much nutrition as possible 

 from the food " (Newton, 1893, 

 p. 187). 



There is a great diversity 

 as regards the caeca, as has 

 been shown in detail by Mag- 

 nan (191 1 ). They are absent 

 in parakeets and some horn- 

 bills. In the latter the mucous 



