138 



DIGESTIVE SYSTEM 



stomach and ends at the cloaca. It may be conveniently divided 

 into (1) the duudemim or first loop, (2) the ileum or narrowest and 

 longest portion, equivalent to both the jejunum and ileum of man, 

 and lastly (3) the redum, corresponding Anth his large intestine. 

 The transition from the ileum to the rectum is marked by a more 

 or less circular valve (the " ileo-csecal "), so placed as to permit its 

 contents to pass into the caeca and rectum, but to hinder their 

 return — their passage throughout the whole intestine being aided by 

 the peristaltic contractions of the muscular layers of its walls. An 

 epithelium of cylindrical cells, forming a colourless, structureless 

 and soft cuticle, lines nearly the whole of the intestine, and is 



P.G., 



Diagram of the Digestive Organs of a Bird. 

 T. Tongue ; P.G. L.G. Parotid and salivary glands ; Tr. Trachea ; I.Br. r.Br. left and right 

 bronchus ; Cr. Crop ; Pr. Proventriculus or glandular stomach ; g. Gizzard or iimscular stomach ; 

 Py. Pylorus ; D. Duodenum ; X. Liver with gall-bladder and duct ; Pa. Pancreas with duct ; 

 C. Caeca ; E. Rectum ; A'. Kidney with Ureter oiiening into the middle cloacal chamber. 



perforated by numerous small pores, oiiening upon their interstices. 

 In many parts these cells form very simple and sometimes tubular 

 glands (" Lieberkiihn's "), and the greater portion of the walls is 

 beset with the villi mentioned above. These are very numerous, 

 and are arranged in various ways — being either uniformly and 

 thickly spread over the surface, giving it a velvety appearance, or 

 are longer and more sparingly distributed in lines, which may be 

 straight or zigzag, transvei'se or longitudinal. Their arrangement 

 is occasionally charactei'istic of different groups of birds ; but it 

 varies also in different parts of the gut. As a rule they are largest 

 and most numerous in the duodenum, but sometimes in the rectum 



