102 AVES. 



the oesophagus is much wider than the gizzard ; the latter is very 

 thin and membranous, as in the Divers. It is very rarely, as in 

 Euphone violacea, that all traces of a muscular stomach or gizzard 

 are wanting. On the contrary, there occurs occasionally, as in the 

 Herons and Pelican, though not in the genus Sula, so nearly allied 

 to the latter, a third always smaller gastro-pyloric dilatation, which is 

 tolerably distinct, and conducts by a narrow pyloric opening into the 

 duodenum. 



The Intestinal Canal always makes a number of convolutions 

 upon itself that are retained in their place by mesenteric folds of 

 peritoneum ; the latter membrane does not, however, develop true 

 omenta. The duodenum forms at its commencement a long loop, 

 within which the pancreatic gland is situated, while the small intes- 

 tine is continued at its lower extremity into a large intestine not 

 much wider, but shorter, and passing downward in front of the ver- 

 tebral column, its commencement being usually indicated by a sym- 

 metrical pair of short or longer cceca coli. The large intestine ter- 

 minates by opening into a wide sacciform or rather bladder-shaped 

 compartment of the urethro-sexual cavity, the cloaca. The villi of 

 the small intestine are generally much elongated, and extend also 

 occasionally as far as the extremities of the cceca, e. g. in Fulica, but 

 this is not the case in the Gallinae and Owls. The villi are, how- 

 ever, frequently wanting, or rather, there occur instead zigzag folds 

 of the lining membrane, as in Corvus, Euphone, Turdus, and perhaps 

 in the Passeres generally. 



Many varieties occur in reference to the two cceca just alluded to. 

 They are, for example, completely wanting in nearly all the Scan- 

 sores and Picariae, as Picus, Psittacus, Rhamphastos, Alcedo, Upupa, 

 Cypselus ; they are very short in the Pigeons, Owls, most Passeres, 

 and many Grallae, e. g. the Stork and Spoon-bill, somewhat longer 

 generally in the Diurnal birds of Prey, while they attain, on the 

 other hand, a considerable development in most of the .Natatores, 

 as the Geese, Ducks, &c., where they are frequently also asymmet- 

 rical, being longer upon one side than the other. The cceca are of 

 surprising length and width in the Gallinae, as in Tetrao, where they 

 each measure a yard in length ; in the Ostrich the cceca are upward 

 of two feet long, provided internally with a spiral valve, and blend, 

 at their inferior extremity, into a single cavity ; the large intestine 

 is here also, as an exception, much longer than the small intestine. 

 It is very rarely that, as in the Mammalia, a single, and in such 



