MARSUPIALIA. 529 



pouch in which the single egg is placed, Australia, Tasmania, N. Guinea ; 

 E. aculeata Shaw. Proechidna Gervais (1877), Xew Guinea, usually with 

 three clawed digits on each limb and traces of the other digits. 



Fam. 2. Ornithorhynchidae. Covered with a dense soft fur ; with 

 the facial portion of the snout broad and elongated and covered with a 

 leathery skin produced into a fold at the base of the snout ; with horny 

 molar teeth in old specimens and true teeth up to half growth (p. 527) ; 

 feet webbsd, with 5 clawed toes, the web on the fore foot extending beyond 

 the claws ; they are aquatic in habit, and form burrows in the banks of 

 streams, with two openings, one above and one below the water ; they 

 are believed to lay two eggs in a nest in the burrow. Australia and Tas- 

 mania. Ornitherhynchus Blumenb. (1800), water mole, duck-billed Platy- 

 pus ; O. anatinus Shaw. 



Order 2. MARSUPIALIA.* 



(Sometimes called Metaiheria, or Didelphia.) 



Mammalia with various dentition and epipubic (marsupial) 

 bones. The mimmary glands have teats which are usually enclosed 

 in a marsupial pouch in which the young are carried. An allantoic 

 placenta is usually absent. 



The principal characteristic of the Marsupials is the possession 

 by most of them of a sac or pouch (marsupium) which is supported 

 by two epipubic (marsupial) bones (Fig. 276), encloses the 

 teats of the mammary glands, and receives the helpless young 

 at birth. Birth takes place at an early stage of development. 

 Even in Macropus giganteus, the males of which attain almost 

 the height of a man, the period of gestation does not last more 

 than thirty- nine days, and the embryo at birth is blind and 

 naked, and not much more than an inch in length. It is 

 placed in the pouch by the mother, sucks firmly on to one of 

 the teats, and remains in the pouch for a considerable period. 

 As additional characters may be mentioned the double 

 vagina, the position of the scrotum in front of the penis, the 

 inclusion of the anus and of the opening of the urinogenital 

 sinus by a common sphincter, the vacuities in the palate, the 

 participation of the alisphenoid in the tympanic bulla, the 

 inflection of the angle of the lower jaw, the absence of the 

 corpus callosum, the absence of a fossa ovalis from the auricular 



* Owen, " Marsupialia," in Todd's Encyclopaedia of Anat. and Physiol. 

 1847. Waterhouse, Natural History of Mammalia, 1, London, 1846. Oldfield 

 Thomas, British Museum Catalogue of Marsupialia and Monotremata, 

 London, 1888. R. Lydekker, Handbook to the Marsupialia and Mono- 

 tremata, in Allen's " Naturalists' Library," 1894. Bensley, Involution 

 of the Australian Marsupialia, etc., Trans. Lin. Soc. (2), 9, p. 83. 



z II M M 



