VERT EB HAT A. 



a few aquatic forms ; excepting the Whales, eacli digit car- 

 ries a nail, claw, or hoof; the teeth (always present, save 

 in certain low tribes) are planted in 

 sockets ; the mouth is closed by flexi- 

 ble lips ; an external ear is rarely ab- 

 sent; 174 the eyes are always present, 

 though rudimentary in some burrow- 

 ing animals ; they are viviparous ; 

 and, finally, and perhaps above all, 

 while in all other animals the embryo 

 is developed from the nourishment 

 laid up in the egg itself, in Mammals 

 it draws its support, almost from 

 the beginning, directly from the 

 parent, and, after birth, it is sus- 

 tained for a time by the milk se- 

 creted by the mammary glands. 

 From the first, therefore, till it can 

 care for itself, the young Mam- 

 mal is in vital connection with the 

 parent. 



d \ 



FIG. 329. Longitudinal Section 

 of Human Body (theoretical) : 

 a, cerebro-spinal nervous sys- 

 tem ; 6, cavity of nose; c, cav- Fio. 330. Transverse Section of Human Body 

 ity of month; d, alimentary (theoretical): a, cerebro - spinal nervons axis 

 canal; e, chain of gympathet- contained in neural tube; e, chain of sympn- 

 ic ganglia; /, heart; g, dia- thetic ganglia; d, alimentary canal; /, heart ; 

 phragm. h, haemal tube. 



SUBCLASS I. Ornithodelphia. 



These Mammals have but one outlet for the intestine, 

 urinary and reproductive organs, as in Birds. They are 

 iinplacental. There is but one order. 



