XIIT 



PHYLUM CHORDATA 



573 



paunch (&), the cardiac compartment of the stomach, with a smooth, 

 thick, mucous membrane. This is followed by a second chamber 

 (c), of considerably smaller dimensions, with a glandular mucous 

 membrane, which is thrown into a number of complex folds. A 

 long and narrow third, or pyloric, compartment (d, e) follows upon 

 this, terminating in a constricted pyloric aperture, beyond which 

 the beginning of the intestine is dilated into a bulb. 



A caecum, situated at the junction of the large and small intes- 

 tines, is usually present, but varies greatly in extent in the different 

 orders and families. It is much larger in vegetable-feeding than 

 in carnivorous forms, and among the former it is those that have 



FIG. 1200. Diagrammatic section of the stomach of the Porpoise, a, oesophagus ; 6, left or 

 cardiac compartment ; c, middle compartment ; d and c, the two divisions of the right, or 

 pyloric compartment ; /. pylorus ; g, duodenum, dilated at its commencement ; h. bile- 

 duct. (After Flower and Lydekker.) 





a simple stomach, such as the Rabbit, that have the largest caecum. 

 Hyrax differs from all the rest of the class in having a pair of 

 supplementary caeca situated some distance down the large intestine. 

 A cjocum is absent in the Sloths, some Cetacea, and a few 

 Garni vora. 



The Prototheria resemble Reptiles, Birds, and Amphibia, and 

 differ from other Mammals, in the presence of a cloaca, into which 

 not only the rectum, but the urinary and genital ducts open. In 

 the Marsupials, a common sphincter muscle surrounds both anal 

 and urinogenital apertures; in nearly all the Eutheria (cf. 

 p, 447) the apertures are distinct, and separated from one 

 another by a considerable space the perinccum. 



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