223 AVES. 



the esophagus ; a membranous stomach, in the thickness of 

 whose parietes are a multitude of glands whose juices humect 

 the aliment ; and finally, the gizzard, armed with two power- 

 ful muscles, united by two radiated tendons, and lined inter- 

 nally with a cartilaginous kind of velvet. The food is the 

 more easily ground there, as birds constantly swallow small 

 stones, in order to increase its triturative power. 



In the greater part of the species which feed exclusively 

 on flesh or fish, the muscles and villous coat of the gizzard 

 are greatly attenuated; and it seems to make but a single sac 

 with the membranous stomach. 



The dilatation of the crop is also sometimes wanting. 



The liver pours its bile into the intestine by two ducts, 

 which alternate with the two or three through which the 

 pancreatic fluid passes. The pancreas of Birds is large, but 

 their spleen is small ; the epiploon is wanting; its functions, 

 however, are partly fulfilled by the partitions of the air cavi- 

 ties ; two blind appendages are situated near the origin of the 

 rectum, and at a short distance from the anus ; they are longer 

 or shorter, according to the regimen of the genus. In the 

 Herons it is short ; in other genera, that of the Woodpeckers 

 for instance, it is totally deficient. 



The cloaca is a pouch, in which the rectum, ureters, sper- 

 matic ducts, and in the female, the oviduct, terminate; it 

 opens externally, by the anus. Strictly speaking, Birds do 

 not urinate, as that excretion mingles with their solid excre- 

 ment. In the Ostriches alone, is the cloaca sufficiently dilated 

 to allow of an accumulation of the urine. 



In most genera, coition is eff'ected by the simple juxta- 

 position of the anus ; the Ostriches, and several of the Palmi- 

 pedes, however, have a penis furrowed with a groove, through 

 which the semen passes. The testes are situated internally, 

 and near the lungs ; only one oviduct is developed ; the other 

 is reduced to a small sac. 



The egg, detached from the ovary, where it consists merely 

 of yolk, imbibes that external fluid, called the white, in the 

 upper part of the oviduct, and becomes invested with its shell 

 at the bottom of the same canal. The chick contained within 



