258 ZOOLOGY. 



and are distinguished chiefly by their mode of development. 

 At birth they are already provided with all their organs, and 

 before birth they derive their nourishment from the mother 

 by means of a placenta. Their brain is more perfect than 



Fig. 218. Caucasian Kace. 



the didelphian, by the presence of a corpus callosum uniting 

 the two cerebral hemispheres ( 186). Finally, the walls of 

 the abdomen have no osseous supports attached to the margins 

 of the pelvis, as we find in the second great class of mam- 

 mals. The mammals thus organized have been subdivided 

 into two groups, namely, ordinary mamjnals and pisciform 

 mammals. 



411. The ordinary mammals are organized principally 

 to live on solid ground ; the skin is provided with hairs. 

 These animals are further subdivided into ten orders : the 

 bimana, quadrumana, cheiroptera, insectivora, rodentia, eden- 

 tata, carnivora, amphibia, pachydermata, and ruminaritia. 

 The first eight of these orders have flexible fingers and toes, 

 with nails covering only the dorsal aspect of the toe or finger, 

 and comparatively small; hence they have been called ungui- 

 culata ; the last two, namely, the pachydermata and rumi- 



