128 THE HUMAN SPECIES 



a cardiac zone double as broad as that of man. The entire 



thickness of the mucous membrane of the human stomach is : 



In the cardia . . . o'37 to 0^56 mm. 



middle as much as i ,, 



pylorus,, r 6 to 2'2 



In the fundus of the human stomach the thickness of the 

 mucous membrane, including the muscularis mucosae, measures 

 from O'8 to o~g mm., the depth of the pit of the stomach from 

 O'l 2 to O'l 3 mm. In the intermedian zone the extent of the gland 

 tubes in various functional states measures approximately 3 to 4 

 cm. ; the extent of the pyloric gland zone approximately 6 cm. 



The intestine of the vertebrates, so important for the pro- 

 cess of digestion, is in the fishes sometimes straight and some- 

 times coiled ; in the amphibians, reptiles and birds it forms 

 a coiled tube varying in length. Its length varies also in 

 mammals according to the form of food. The mucous mem- 

 brane is usually transversely folded and abundantly provided 

 with villi ; the muscular tissue is, with few exceptions, smooth. 

 The muscularis mucosae possesses, internally, circular, externally, 

 longitudinal fibres, the latter alone being continued into the large 

 intestine where the ileum passes into the caecum, while the 

 circular stratum is completely absorbed in the valvula Banhini. 



Characteristic of man and the ruminants, though of none 

 of the other domestic mammals, as of the anthropoids (Owen, 

 Virchow), are the closely placed, transverse folds which among 

 the birds occur in similar form only in the Struthionidae 

 (Ellenberger). 



The intestinal villi are largest in the carnivora, whereupon 

 follow man and the horse, and, lastly, among the domestic 

 mammals, the ruminants and the pig. The villi of the human 

 intestines are on the whole not broad and but moderately oblate. 



Their proportions are : 



In the Duodenum and Jejunum, 0*6 to O'8 mm. long 



In the Ileum; 



1 Ellenberger, loc. cit., p. 692. 



