138 DIGESTIVE (S VSI 
stomach and ends at the cloaca. It may be conveniently divided 
into (1) the duodenum or first loop, (2) the dewn or narrowest and 
longest portion, equivalent to both the jejunum and ileum of man, 
and lastly (3) the rectum, corresponding with his large intestine. 
The transition from the ileum to the rectum is marked by a more 
or less circular valve (the “‘ileo-cxecal”), so placed as to permit its 
contents to pass into the ceca 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 
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DIAGRAM OF THE DIGESTIVE ORGANS OF A BIRD. 
T. Tongue; P.G. L.G. Parotid and salivary glands; Tr. Trachea; 1.Br. r.Br. left and right 
bronchus ; Cr. Crop; Pr. Proventriculus or glandular stomach ; g. Gizzard or muscular stomach ; 
Py. Pylorus; D. Duodenum; L. Liver with gall-bladder and duct; Pa. Pancreas with duct; 
C. Ceca; R. Rectum; K. Kidney with Ureter opening into the middle cloacal chamber. 
perforated by numerous small pores, opening upon their interstices. 
In many parts these cells form very simple and sometimes tubular 
glands (“ Lieberktihn’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, transverse or longitudinal. Their arrangement 
is occasionally characteristic 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 
