230 COMPARATIVE MORPHOLOGY OF VEGTEBRATES. 
The intestine is longer in the birds than in the reptiles, but there is considerable 
difference in the group in this respect. The great increase comes in the colon which 
is coiled in different ways, which may be reduced to seven plans or combinations 
of loops and spirals (fig. 234). In a few forms (woodpeckers, parrots, etc.), there 
Ivegey any 
Fic. 234.—Types of coiling of the intestines of birds, after Gadow. A, isoccelous; 
B, anticcelous; C, antipericcelous; D, isopericcelous; E, cycloccelous; F, plagioccelous; G, 
telogyrous; p, pylorus. : 
is no cecum, but usually the junction of large and small intestine is marked by one 
or two ceca (fig. 235). In some cases these ceca are lined with villi, or portions 
may be ciliated, while the very large caecum of the ostrich is spirally coiled. Many 
birds have a pocket, the bursa Fabricii, of unknown functions, developed from the 
Fic, 235.—Alimentary canal of Chauna, after Mitchell. c, ceca; /, large intestine; p 
Econ: pv, portal vein; rv, rectal vein; s, small intestine; v, remnant of vitelline 
uct. 
dorsal part of the cloaca. It arises from the ectodermal (proctodeal) portion and 
extends forward, dorsal to the rectum (fig. 236). In some cases it degenerates in 
the adult. 
The limits of large and small intestine in the mammals are usually marked by an 
ileo-colic valve and a single cecum, but there are two ceca in some edentates, 
while some edentates, bats, carnivorous mammals and many whales lack either 
cecum or valve. The cecum is larger in the herbivorous forms and frequently 
