136 COMPARATIVE ANATOMY. 



Nipples are four in number in Macropus (kangaroo), concealed 

 within fissure in Cetacea, absent in Ornithorhynchus.* With 

 some mammals the glands are situated in the ventral region, 

 as in Sus (hog), restricted to inguinal region, as in Ruminan- 

 tia, while with others they are exclusively confined to the 

 pectoral, as in Cheiroptera (bat), Quadrurnana, and man. 



* The cow, ewe, goat, guinea-pig, and porpoise have one tube in each teat. 

 The pig has two, the rhinoceros has twelve, and the hare and rabbit, and the 

 cat and bitch have several. In the Ruminantia the reservoirs (ampullae) are 

 enormously enlarged, with Carnivora comparatively small. In the pig there 

 is scarcely any reservoir; in the porpoise the great enlargement of the milk 

 tube is a substitute for the reservoir. (Astley Cooper.) 



