510 MAMMALIA. 



the rodents, apes, etc., dilated into wide sacs — the so-called 

 cheek-pouches. The soft palate (palatum molle) must be men- 

 tioned as a structure peculiar to the Mammalia ; it constitutes 

 the boundary between the buccal cavity and pharynx. All 

 mammals, with the exception of the carnivorous Cetacea, have 

 salivary glands, — a parotid, a submaxillar}^, and a sublingual, — 

 the fluid secretion of which is poured out in large quantities, 

 especially in herbivorous forms. The oesophagus, which follows 

 the wide gullet, only exceptionally presents croj^-like dilations ; 

 it is usually of considerable length, and opens into the stomach 

 behind the diaphragm. The stomach is, as a rule, a simple 

 transversely placed sac, but is frequently divided bj^ the gradual 

 dift'erentiation and constriction of its anterior, lateral, and j)OS- 

 terior regions into a number of parts, which are most completely 

 separated in the ruminants and distinguished as four separate 

 stomachs. The pyloric region is principally distinguished by 

 the presence of gastric glands, and is more or less sharply sepa- 

 rated from the beginning of the small intestine by a sphincter 

 muscle and by an inwardly projecting fold (pyloric valve). The 

 intestine is divided into a small and a large intestine, the boun- 

 dary between which is indicated by the presence of a valve and 

 a caecum, which is especially developed in herbivorous animals. 

 The anterior part of the small intestine, or duodenum, contains 

 the so-called Brunner's glands in its mucous membrane, and 

 receives the secretion of the large liver and the pancreas. The 

 liver is multilobed, and is sometimes without a gall bladder. 

 When a gall bladder is present the bile duct (d. cysticus), and 

 the hepatic duct (d. hepaticus) unite to form a common duct 

 (d. choledochus). The small intestine is longest in animals 

 which eat grasses and leaves, and is characterised by the numer- 

 ous folds (valvulae conniventes) and villi of its mucous mem- 

 brane; and by the possession of a great number of groups of glands 

 (Lieberkuhn's) and by Peyer's patches which are composed of 

 adenoid tissue. The terminal region of the large intestine or 

 rectum opens, except in the Monotremata which are character- 

 ised by the possession of a cloaca, behind the urinogenital opening, 

 though the two openings are sometimes surrounded by a common 

 sphincter (Marsupialia, some Insectivora and Pinnipedia). 



The heart (Fig. 268) of Mammalia, like that of Birds, is divided 

 into a right venous and a left arterial portion, each with a ven- 



