DIGESTIVE SYSTEM. 43 



the Sheep even as 28 to 1 ; in most Carnivora, it is as 4 to 1 ; and 

 in the Cheiroptera, as 3 to 1. Many animals, as the Cetacea, the 

 Ornithorynchus, and the Mole, seem to have mere longitudinal folds 

 upon the mucous membrane, but no villi. 



Of the Salivary glands the three pairs of the human subject are 

 generally present, yet they are wanting completely in the Cetacea. 

 The Dugong (Halicore) alone has a very large parotid, which on the 

 other hand is wanting along with the sublingual gland in the Seals. 

 These glands are also partly wanting in the Monotremata. In gen- 

 eral the salivary glands are largely developed in the Ruminantia, 

 Pachydermata, and Rodentia, moderately so in the Quadrumana, and 

 less in the Carnivora. In many Carnivora, as in the Dog, and in 

 many Rodentia, as the Squirrel, and also in the Makis, the submaxil- 

 lary glands are larger than, frequently as large again as the parotids. 

 This is especially the case in the Beaver, where the two coalesce 

 posteriorly in the nape of the neck, and form a large mass. The 

 Edentata, also, especially the Kangaroo and Opossum, as likewise 

 the Cheiroptera, have large salivary glands, with the exception of the 

 sublingual, which, in the last-named order, is very slightly developed ; 

 in the Dog and Cat it is also very small. The submaxillary gland 

 is very large in Myrmecophaga and Orycteropus. 



The Liver of the Mammalia is fashioned after the human type ; it 

 is usually divided into two principal lobes, and is frequently more 

 deeply bisected. In the Cetacea its two lateral lobes are very feebly 

 indicated; in the Ruminantia there is found a third smaller lobe. 

 The liver is three-lobed in the Hog and some Rodentia j most of the 

 Rodentia, Marsupiata, and Apes, have, however, from 4 to 6, the Car- 

 nivora still more, 6 to 8 lobes, as the Dog, Cat, and Bear. The 

 liver of the Orang is like that of Man. 



The Gall-bladder is usually present, though it is also frequently 

 wanting, as, for example, in the true Cetacea, many Ruminantia 

 (Camel, Goat), the Horse, and most Pachydermata (though not in 

 the Hog), and several of the Rodentia, as the Hamster, the 'Mouse, 

 and in the Sloth among the Edentata. A biliary duct always passes 

 to the intestine, into which, or into the gall-bladder, the excretory 

 ducts of the liver pour their secretion. The pancreatic duct often 

 joins just before it enters the intestine the termination of the biliary 

 duct, which is in this situation frequently expanded in the shape of a 

 bladder, as in the Elephant, the Kangaroo, the Otter, the Seal, &c. 

 A remarkable peculiarity is possessed by the Orycteropus, in which 

 two separate gall-bladders occur, united by a common peritoneal 



