486 MANUAL OF ZOOLOGY. 



corresponds with the division of the "Placental" Mammals, 

 and includes all the Mammalia except the Monotremes and 

 Marsupials. 



Before going on to consider the different orders of the Mam- 

 malia in detail, it may be as well very briefly to run over the 

 leading characters by which the various orders are distinguished : 



Order I. Monotremata, characterised by the fact that the 

 ureters and ducts of the reproductive organs open into a com- 

 mon urogenital canal, which in turn opens, along with the 

 rectum, into a " cloaca." The testes are abdominal, and are 

 not lodged in a scrotum. The mammary glands have no 

 nipples. The young is devoid of a placenta, but the female 

 possesses no marsupial pouch, though the pelvis is furnished 

 with " marsupial bones." In this order are only the Duck- 

 mole and the Echidna. 



Order II. Marsupialia, characterised by the fact that the 

 uterine dilatations of the oviducts open with the ureters into a 

 urogenital canal, which is distinct from the rectum, though 

 embraced by the same sphincter muscle. The testes are not 

 abdominal, but are lodged in a scrotum which is suspended 

 by a narrow neck in front of the penis. The females are 

 mostly furnished with a marsupial pouch, in which the young 

 are carried for some period after birth. The young are not 

 provided with a placenta, and are born in a very imperfect 

 state of development. Marsupial bones are present. In this 

 order are the Kangaroos, Opossums, Wombats, &c. 



Order III. Edentata or Bruta, characterised by the univer- 

 sal absence of the median incisors, and the general absence 

 of all the incisors. The canines are usually wanting as well, 

 and sometimes there are no molars either. There is only one 

 set of teeth, and the teeth have neither complete roots nor are 

 furnished with a covering of enamel. The toes are always 

 furnished with claws. Placenta sometimes deciduate, some- 

 times non-deciduate. As examples of this order may be taken 

 the Sloths, Armadillos, and the great Ant-eater. 



Order IV. Sirenia, comprising the Dugongs and Manatee, 

 characterised by being adapted to an aquatic life. Body fish- 

 like, with a strong horizontal tail-fin. There is no sacrum, 

 and the hind-limbs are invariably wanting, whilst the fore- 

 limbs are converted into swimming-paddles. There are, in 

 the living forms at any rate, two sets of teeth, and the molars 

 have flattened crowns adapted for a vegetable diet. There are 

 two nostrils, and these are placed at the upper part of the 

 snout. There are two mammae, and these are placed on the 

 chest, and not on the abdomen. 



