386 The Feeding of Animals 



a general resemblance to the mammalian form, they do 

 not clearly show the same divisions. The diameter is 

 about the same throughout. The ca3ca, each of which 

 is closed at one end and opens into the intestines at 

 the other, seem to be important and essential modifi- 

 cations of that canal. Each caecum is from six to 

 seven inches long in mature fowls. Not far from the 

 openings of the caeca the intestine ends in a dilatation, 

 the cloaca, into which the genito- urinary passages also 

 open. It is because of the mixing here of the undi- 

 gested residues of the food with the secretions from 

 the kidneys and with some other products of metabolism, 

 that an accurate estimation of the digestibility of food 

 by birds is so difficult. No satisfactorily accurate 

 methods for separating some of the nitrogenous resi- 

 dues from different organs seem yet to be perfected. 



Into the intestine shortly after it leaves the gizzard 

 two ducts from the liver and two from the pancreas 

 enter, discharging the bile and pancreatic juices. The 

 liver, as usual, is a large organ. The pancreas also is 

 very largely developed, and extends for several inches 

 along the duodenal loop of the intestines, reaching in 

 the common fowl a length of over five inches. 



Altogether the structure of the digestive apparatus 

 of birds indicates extreme efficiency and the capacity 

 for rapid work. A study of it suggests, also, as does 

 that of any complicated and delicately adjusted appa- 

 ratus, that it should not be overloaded nor violently 

 disturbed when running at high pressure. It may be 

 said to run at high pressure while the extremely rapid 

 growth of young birds occurs, and during the extended 



