DIGESTIVE SYSTEM. 103 



cases invariably shorter, coecum is present, as in the whole genus of 

 Herons. 



There is not unfrequently found, about the middle of the small in- 

 testine, a small coecum or diverticulum, which indicates the former 

 place of entrance of the vitelHne duct into the intestine. This per- 

 sistent remnant of an embryonic structure is remarkably constant and 

 normal in many of the Grallae arid Palmipedes,, as the Goose, while it 

 is scarcely ever to be perceived in the orders Rapaces, Passeres, and 

 Scansores. 



The whole intestinal canal is of very variable length, being 

 scarcely double as long as the body in Mormon fratercula, while in 

 the Penguin it is fifteen times its length. 



The Salivary Glands vary greatly in number and development 

 throughout the several orders and even genera of birds, in accord- 

 ance with their mode of life. In general four pairs of these glands 

 are to be met with, namely, a pair of sublingual glands situated upon 

 either side beneath the tongue, two submaxillary glands divided 

 each into an anterior and posterior, which lie the one behind the 

 other, and open by special ducts in front of the lingual organ, and a 

 gland that may be compared to the parotid, which is placed close 

 beneath the skin upon the angle of the mouth, and frequently extends 

 into the orbitar cavity. Occasionally one or the other pair of the 

 above glands are wanting, and in Sula, Carbo, Phcenicopterus, they 

 appear to be all of them absent, or, as in the Grallae and Palmipedes 

 generally are but slightly developed. In the Geese and Ducks all 

 the pairs, however, are met with, and in the Goose the sublingual 

 gland is of particularly large size. The Herons possess only the 

 sublingual gland. In the Watercoot (Fulica), and still more so in 

 Hirundo esculenta, the parotid gland is very much developed, and 

 in the latter bird its secretion serves for the preparation of their edi- 

 ble nests ; in the Rapaces, Passeres, and Gallinae, the salivary glands 

 are generally all present. In the Woodpecker and Wryneck '(Yunx) 

 the anterior and posterior submaxillary glands are constantly blended 

 into a large, white, and flattened gland, which secretes a very vis- 

 cous salivary fluid. 



The Liver, which is of a brownish red color, is divided always 

 into two halves or lobes, of equal or else very unequal size. In the 

 Rapaces, many Grallae and Palmipedes, both lobes of the liver are 

 of equal magnitude, while in the Passeres the left lobe is generally 

 much smaller than the right. The Gall-bladder is absent only in 

 a few genera, as in the Ostrich, the Pigeons, and many of (though 



