368 CLASSIFICATION OF VERTEBRATES. 



which reference must be made to histological text -books. On the 

 basis of these glands the stomach may be divided into regions, 

 when it is seen that in the monotremes the morphological stom- 

 ach is entirely lacking, the enlargement which occurs being 

 resophageal. More frequently the cardiac glands are lacking. 



Speaking of the stomach in the more usual sense, it may be 

 said that usually its axis lies at right angles to the axis of the 

 body, and that only exceptionally, as in the seals, is it longitu- 

 dinal. 1 The stomach may be a simple sac, as in man, but in 

 the cetacea and ruminants it becomes divided into several cham- 

 bers, the extremes of differentiation being reached in the rumi- 

 nants, where (the tylopoda and tragulina excepted) four distinct 

 - regions, the rumen (paunch), reticulum (honeycomb), psalte- 

 rium, or omasum (manyplies), and abomasum may be recog- 

 nized ; but of these only the last is a true glandular stomach, 

 the others being oesophageal enlargements. 



The intestine is differentiated into small and large divisions, 

 the line between them being marked by the ileocolic valve. 

 The first part of the intestine, the duodenum, is characterized 

 by receiving the ducts of liver and pancreas, and also by the 

 presence of Brunner's glands in its walls. The small intestine 

 is greatly convoluted. The large intestine is of larger diameter 

 than the small, and its walls show outsackings or lobulations. 

 It presents two divisions, a rectum, situated in the pelvis, and 

 comparable to the large intestine of the lower vertebrates, and 

 a much longer colon, which appears for the first time in mam- 

 mals. Just beyond the ileocolic valve is a blind diverticulum, 

 the caecum, which undergoes great variations in size. It is 

 largest in the herbivora, where it may equal the body in length, 

 while in the edentates, carnivores, toothed whales, bats, etc., it 

 may be small or even absent. In many rodents, apes, and man, 

 the distal part of the caecum becomes reduced in size, and forms 

 the appendix vermiformis. The rectum terminates, except in the 

 monotremes, in an anus dorsal to the urogenital opening. In 

 that group it and the urogenital system empty into a cloaca as 

 in the sauropsida. 



1 In the seals (Fig. 351 ), it is only the oesophageal part of the stomach that is longi- 

 tudinal, the true stomach being transverse. 



