ALIMENTARY CANAL 31 



sometimes completely absent, as in the majority of that 



large assemblage of birds the picarians, but when present 



they show every degree of relative size. In the Passeres, and 



in some other birds, the two caeca are the merest nipples, 



which cannot be believed to serve any function. They are 



in the same way reduced in size 



in the hawks and storks. On the 



other hand, in the gallinaceous 



birds, in the Limicolae, and in some 



others the caeca are large tubular 



diverticula of the gut, the length 



being sometimes to be measured 



by inches. Among the owls the 



caeca are large, and have the i''i<- i ; j. I'am* major. 



additional peculiarity of being (fiESSteo^S 



swollen at the blind extremity. 



The caeca are most complicated in the ostrich, the screamers, 



and the tinamou Calodromas, under the descriptions of which 



birds will be found an account of this organ. The herons 



are remarkable for the fact that one of the two casca has 



disappeared, the remaining one being but small. 



The liver is invariably composed of two lobes, of which 

 the left often shows a more or less distinctly marked 

 secondary division. The size of the lobes varies greatly, as 

 does their relative size. Thus in some birds the liver lobes 

 are quite hidden by the sternum ; in others again they 

 descend some w r ay down below the shelter of that bone and 

 are apparent when the muscular walls of the abdomen are 

 cut through or removed. The two lobes are occasionally 

 equal or subequal in size ; more generally there is a dis- 

 crepancy, the right or left, as the case may be, being the 

 larger, sometimes very much the larger. The two lobes of 

 the liver are commonly firmly attached to each other by a 

 bridge of hepatic tissue. In Chauna they are nearly separate, 

 being only united by a very narrow isthmus of liver substance. 

 The liver sometimes (e.g. mRhynchotus rufescens) has two or 

 three small vessels, belonging to the portal system, entering 

 its substance at the free edge, a state of affairs which has a 



