552 MANUAL OF ZOOLOGY. 



enlargements of the oviducts coalesce to a greater or less 

 extent to form a single uterine cavity, which, however, generally 

 shows its true composition by being divided superiorly into 

 two cornua. The uterus opens again into a single vagina, 

 which is always distinct from the rectum. This sub-class 

 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 

 Mammalia 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. Strenia, comprising the Dugongs and Manatees, 

 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- 



