5 i8 MANUAL OF ZOOLOGY SECT. 



fibres, the pons Varolii, by which the lateral portions of the 

 cerebellum are connected together. 



The ureters, except in the Prototheria, open into the 

 bladder. 



With the exception of the Prototheria, Mammals are all 

 viviparous. The foetus is nourished before birth from the 

 blood-system of the parent through a special development 

 of the allantois and the lining membrane of the uterus, 

 termed the placenta. After birth the young Mammal is 

 nourished for a longer or shorter time by the milk or 

 secretion of the mammary glands of the parent. 



The class Mammalia is divisible into two main divisions 

 or sub-classes, the Prototheria and the Theria. 



The Prototheria are Mammals in which the mammary 

 glands are devoid of teats ; the oviducts are distinct through- 

 out, and there is a cloaca into which the ureters and the 

 urinary bladder open separately. In the centra of the 

 vertebras the epiphyses are absent or imperfectly developed ; 

 the bones of the skull early coalesce by the obliteration of 

 the sutures ; there is a large coracoid articulating with the 

 sternum, a T-shaped episternum, and a pair of epipubic 

 (marsupial) bones. In the brain a corpus callosum is 

 absent. The ova are discharged in an early stage of their 

 development, enclosed in a tough shell. 



This sub-class comprises a single living order, the Mono- 

 tremata, including the Duck-Bill or Platypus (Ornitho- 

 rhynchus} and Spiny Ant-eater (Echidna}. 



The Theria are mammals in which the mammary glands 

 are provided with teats ; tho oviducts are united in a longer 

 or shorter part of their extent, and there is no cloaca ; the 

 ureters open into the base of the bladder. The centra of 

 the vertebrae possess distinct epiphyses ; the bones of 

 the skull in most instances do not completely coalesce, 



