14 THE DISEASES AND DISORDERS OF THE OX. 



betwixt the circulating fluids of the mother and those of the 

 foetus. This organ, the placenta, varies widely in shape and 

 structure in the various minor divisions of the sub-class Mono- 

 delphia, which, we may mention, includes the following ten 

 orders, namely: Primates (man and monkeys) ; Chiroptera 

 (bats) ; Insectivora (hedgehogs, shrews, moles, &g.) ; Carnivora 

 (cats, dogs, bears, seals, walruses, sea-lions) ; Cetacea (whales, 

 cachalots, narwhals, dolphins, porpoises) ; Sirenia (manatee and 

 dugong) ; Ungulata; Hyracoidea (hyrax) ; Proboscidea (elephant) ; 

 Rodentia (hares, rats, guinea-pigs, porcupines, beavers, squirrels, 

 &c). Another group may be placed apart from the rest. This 

 is the order Edentata, which includes the sloths, the armadillos, 

 the ant-eaters of America, the pangolins and orycteropus. 



Of the mammals, those which may be said to be domesti- 

 cated are the horse, ass, ox, sheep, goat, camel, llama, pig, 

 elephant, dog, cat, and rabbit. Of the above the first eight 

 belong to the order of the Ungulata, or animals provided with 

 hoofs. The camel, llama, and elephant cannot be said, in any 

 strict sense of the term, to be domesticated in Europe. The ox, 

 of course, comes under this order of hoofed quadrupeds. 



In the Ungulata the whole surface of the allantois is covered 

 with villi, and the placenta is thus diffuse. Of the earliest known 

 representatives of these animals some resembled the Ptodents, 

 while others tended rather to approach the characters presented 

 by the Insectivora. With the exception of the musk-deer, hoofed 

 animals are as a rule of large size. Moreover, they are all 

 terrestrial animals, and all are herbivorous ; but some, e.g. the 

 pig, are omnivorous. With regard to dentition, we may say that 

 there is nearly always an interval or diastema in ungulate ani- 

 mals between the incisor and the molar teeth. Usually ail three 

 kinds of teeth are present ; but the canines frequently disappear. 

 As our readers well know, the horse possesses canine teeth, 

 though the mare does not. Large molar teeth are always 

 present. 



Ruminants have their teeth arranged as follows : — 



Upper iaw) . . . , , 5,7 



T ^^ • > incisors canines molars from to 



Lower jawf 3 1 5 7 



The canine is developed especially in males, and it is often 

 pushed up into close proximity with the incisors. The Bovidae, 



