CLASSIFICATION. MAMMALIA. CLASSIFICATION. 



tingnished from the rest of the mammals by the very 

 imperfect condition in which the young are born. In 

 the ordinary mammals, when the embryo has attained 

 a certain degree of development, a vascular body called 

 the placenta is produced, by which the union of the 

 young animal with the mother is greatly increased. 

 This organ is never formed in the animals arranged by 

 Cnvier in his order Marsupialia ; their young are pro- 

 duced in an almost embryonic state, and the mother is 

 usually furnished with an abdominal pouch containing 

 the teats, which serves as a protection to the young 

 animals during their helpless state. This character 

 is referred to in the name given to the order, which 

 is derived from the Latin marsupium, a pouch. In 

 order to give the pouch a firmer support than it could 

 derive from the abdominal muscles, the animals are 

 furnished with a pair of peculiar bones (the marsupial 

 bones), which spring from the anterior part of the pelvis ; 

 the presence of these bones constitutes one of the most 

 important practical characters of the group, as they 

 occur both in the males and females, and even in those 

 species in which the pouch is deficient, or replaced by 

 a mere fold of the skin of the belly. 



Besides these characters, there are others of great 

 importance presented by the structure of the brain, 

 in which, as in their reproduction, the Marsupialia 

 evidently exhibit a marked approach to the oviparous 

 classes of Birds and Reptiles. In most of the Mammalia 

 the two hemispheres of the brain are united, besides 

 other bonds of union, by a large band called the corpus 

 callosum; this is entirely wanting in the marsupials. 

 The hemispheres themselves are smooth and smaller 

 than in other mammals, leaving the olfactory and optic 

 lobes and the cerebellum perfectly visible when the 

 brain is viewed from above ; characters which show a 

 certain resemblance to those of birds. 



Taking the whole of the above peculiarities into consi- 

 deration, nearly all zoologists have not only coincided 

 in admitting the justice of Cuvier's separation of the 



animal, presenting them as a distinct order of mam- 

 mals, but have even gone beyond him, and regarded 

 these creatures, with two singular animals referred by 

 Cuvier to the Edentata, as forming a distinct subclass 

 of mammalia, which has been denominated Aplacen- 

 talia or Acotyledona, from the absence of the placenta, 

 the most striking physiological character exhibited by 

 its members. Most naturalists, although regarding the 

 characters presented by the aplacental mammals as 

 indicative of a lower position in the scale of organiza- 

 tion than that occupied by the rest of the class, have 

 not failed to perceive that in the characters of the den- 

 tition, the limbs, and the general conformation of the 

 body, they present a diversity almost as great as that 

 manifested amongst the Placentalia, so that we find 

 amongst them herbivorous, carnivorous, insectivorous, 

 rodent, and even edentate forms ; and thus arose the 

 idea that the two subclasses of Mammalia were rather 

 to be regarded as parallel and mutually representative 

 series than as truly superior and inferior groups. This 

 notion, carried still further, led some zoologists to ignore 

 the section of aplacental mammals altogether, and to 

 distribute its members amongst those orders and fami- 

 lies of Mammalia with which, in their other characters, 

 they seemed to be most nearly allied. As, however, 

 these views were for the most part promulgated by 

 writers who had some favourite theory of classification 

 of their own to support, they naturally died with the 

 systems which gave them birth, although it is remark- 

 able that in one of the most recent and valuable works 

 on the Mammalia,* we find the toothless aplacental 

 mammals arranged with the Edentata as in the system 

 of Cuvier, whilst the remainder of the subclass still 

 stands as the order Marsupialia. Dr. Gray, of the 

 British Museum, also places the toothless species with 

 the true Edentata, whilst he follows Linnaeus in placing 

 the marsupials amongst the Ferce.^ 



The system that will be adopted in the present work 

 is shown in the following tabular view: 



Subclass I. PLACEXTAL MAMMALS. 



A. Unguiculate or Clawed. 

 Order 1. BIMANA ; the anterior limbs furnished with hands. 



" 2. QUADRUMAXA; furnished with four hands; the posterior thumbs opposable. 



" 3. CHEIROPTERA ; anterior limbs converted into wings, the fingers being very long, and connected by a 



membrane. 



" 4. INSECTIVORA ; four feet formed for walking ; molar teeth broad, with sharp tubercles. 

 " 5. CAKNIVORA ; four feet formed for walking ; molars narrow and sharp. 

 " 6. PJXXIPEDIA : four feet formed for swimming only ; molars narrow and sharp. 

 " 7. RODENTIA ; tour feet fonned for walking ; no canine teeth ; incisors two in each jaw, chisel-shaped. 

 4i 8. EDENTATA ; four feet formed for walking or climbing ; no incisors or canines in either jaw. 



B. Ungulate or Hoofed. 



Order 9. RUMIXANTIA ; hoofs cloven ; incisor teeth wanting in the upper jaw ; stomach complicated. 

 " 10. SOLIDUNGULA \ feet with a single toe and a solid hoof; incisor teeth in both jaws. 



11. PACHYDEUMATA ; 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. APLACEXTAL 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 Savytkiere. 

 f It must be remarked, however, that the few species o 

 family of opossums. 



if marsupial animals known to Linna;u> were all of the ferine 



