Classificatiojs. MAMMALIA. Classification. ^ 
tingiiished from the rest of the mammals by the very 
animal, presenting them as a distinct order of mam- 
imperfect condition in which the young are born. In 
mals, but have even gone beyond him, and regarded 
the ordinary mammals, when the embryo has attained 
these creatures, with two singular animals referred by 
a certain degree of development, a vascular body called 
Cuvier to the Edentata, as forming a distinct subclass 
the placenta is produced, by which the union of the 
of mammalia, which has been denominated Aplacen- 
young animal with the mother is greatly increased. 
talia or Acotyledona, from the absence of the placenta, 
This organ is never formed in the animals arranged by 
the most striking physiological character exhibited by 
Cuvier in his order Marsupialia ; their young are pro- 
its members. Most naturalists, although regarding the 
duced in an almost embryonic state, and the mother is 
characters presented by the aplacental mammals as 
usually furnished with an abdominal pouch containing 
indicative of a lower position in the scale of organiza- 
the teats, which serves as a protection to the young 
tion than that occupied by the rest of the class, have 
animals during their helpless state. This character 
not failed to perceive that in the characters of the den- 
is referred to in the name given to the order, which 
tltion, the limbs, and the general conformation of the 
is derived from the Latin marsupium, a pouch. In 
body, they present a diversity almost as great as that 
order to give the pouch a firmer support than it could 
manifested amongst the Placentalia, so that we find 
derive from the abdominal muscles, the animals are 
amongst them herbivorous, carnivorous, insectivorous. 
furnished with a pair of peculiar bones (the marsupial 
rodent, and even edentate forms ; and thus arose the 
i 
hones'), which spring from the anterior part of the pelvis; 
idea that the two subclasses of Mammalia were rather 
the presence of these bones constitutes one of the most 
to be regarded as parallel and mutually representative 
important practical characters of the group, as they 
series than as truly superior and inferior groups. This 
occur both in the males and females, and even in those 
notion, carried still further, led some zoologists to ignore 
species in which the pouch is deficient, or replaced by 
the section of aplacental mammals altogether, and to 
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a mere fold of the skin of the belly. 
distribute its members amongst those orders and fami- 
Besides these characters, there are others of great 
lies of Mammalia with which, in their other characters, 
importance presented by the structure of the brain. 
they seemed to be most nearly allied. As, however. 
in which, as in their reproduction, the Marsupialia 
these views were for the most part promulgated by 
evidently exhibit a marked approach to the oviparous 
writers who had some favourite theory of classification 
classes of Birds and Reptiles. In most of the Mammalia 
of their own to support, they naturally died with the 
the two hemispheres of the brain are united, besides 
systems which gave them birth, although it is remark- 
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other bonds of union, by a large band called the corpus 
able that in one of the most recent and valuable works 
callosum-, this is entirely wanting in the marsupials. 
on the Mammalia,* we find the toothless aplacental 
The hemispheres themselves are smooth and smaller 
mammals arranged with the Edentata as in the system 
than in other mammals, leaving the olfactory and optic 
of Cuvier, whilst the remainder of the subclass still 
lobes and the cerebellum perfectly visible when the 
stands as the order Marsupialia. Dr. Gray, of the 
, 
brain is viewed from above ; characters which show a 
British Museum, also places the toothless species with 
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certain resemblance to those of birds. 
the true Edentata, whilst he follows Linnaeus in placing 
Taking the whole of the above peculiarities into consi- 
the marsupials amongst the Ferce.^ 
deration, nearly all zoologists have not only coincided 
The system that will be adopted in the present work 
in admitting the justice of Cuvier’s separation of the 
is shown in the following tabular view; — 
Subclass I. — Placental Mammals. 
A. Unguiculate or Clawed. 
j 
Order 1. Bimana ; the anterior limbs furnished with hands. 
“ 2. Quaduumana; furnished with four hands; the posterior thumbs opposable. 
“ 3. Cheiroptera ; anterior limbs converted into wings, the fingers being very long, and connected bt' a 
membrane. 
“ 4. Insectivora ; four feet formed for walking ; 
molar teeth broad, with sharp tubercles. 
“ 5. Carnivora ; four feet formed for walking ; 
molars narrow and sharp. 
“ 6. Pinnipedia ; four feet formed for swimming only ; molars narrow and sharp. 
“ 7. Rodentia ; four feet formed for walking ; no canine teeth ; incisors two in each iaw, chisel-shaped. 
“ 8. Edentata ; four feet formed for walking or 
climbing ; no incisors or canines in either jaw. 
B. Ungulate or Hoofed. 
Order 9. Ruminantia ; hoofs cloven ; incisor teeth wanting in the upper jaw ; stomach complicated. 
“ 10. Solidungul.a ; feet with a single toe and a 
solid hoof ; incisor teeth in both jaws. 
“ 11. Pachydermata ; feet with two or more toes and hoofs ; incisor teeth always in the upper jaw. 
C. Mutilated or Defective. 
Order 12. Cetacea ; body fish-like ; anterior limbs converted into paddles, posterior limbs wanting. 
Subclass II. — Aplacental Mammals. 
Order 13. Marsupialia ; teats inclosed in a pouch, or between two folds of the skin of the belly ; incisor 
and molar teeth always present ; only one clavicle ; external ears. 
“ 14. Monotremata ; with a single outlet or cloaca, for the urinary, generative, and intestinal organs ; 
no pouch or external ears ; teeth wanting or horny in texture ; clavicle double. 
• Professor “Wagner’s Continuation of Schreber’s Saugthiere. 
f It must be remarked, however, that the few species of 
marsupial animals known to Linnaeus were all of the ferine 
family of opossums. 
