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more naturally defined orders, according to various characters afforded by the dental, osseous, generative and locomotive systems, which his great anatomical knowledge had made known to him.

That heterogeneous order which Linnaeus—prepossessed in favour of the easily recognisable outward character by which he distinguished the class—had characterised by the 'Mamma, pectorales bince: dentes primores incisores: superiores iv parallel?,' was shewn, by the correlation of anatomical distinctions with the threefold modification of the limbs of the Primates, to be divisible into as many distinct orders. The hands on the upper limbs alone, and the lower limbs destined to sustain the trunk erect, characterised the order Bimana, the equivalent of the Linnsean genus Homo. The genus Simia of Linnaeus, with hands on the four extremities, became the order Quadrumana of Cuvier. The genus Vespertilio with the 'manus palmatae volitantes' formed the group Cheiroptera, answerable to the Dermaptera of Aristotle.

Ray had pointed out certain viviparous quadrupeds with a multifid foot as being "anomalous species," instancing as such "the tamandua, the armadillo, the sloth, the mole, the shrew, the hedgehog, and the bat." The first three species are associated with the scaly ant-eaters (Manis) of Asia and Africa, with the Australian spiny ant-eaters (Echidna), and with the more strange duck-moles (Ornithorhynchus) of the same part of the world, to form the order Edentata of Cuvier, which answers to that called Bruta by Linnaeus, if the elephant and walrus be removed from it. The rest of Ray's anomalous species exemplify the families Cheiroptera and Insectivora of the Cuvierian system, in which they are associated with the true Carnivora in an order called 'Carnassiers,' answering to the Ferce of Linnaeus.

Cuvier had early noticed the relation of the Australian pouched mammals, as a small collateral series, to the

1 Tom. cit. p. 24.

unguiculate mammals of the rest of the world; 'some,' he writes, 'corresponding with the Carnivora, some with the Rodentia, and others again with the Edentata, by their teeth and the nature of their food.' They formed a family of the Carnassiers in the first edition of the 'Eigne Animal but were raised to the rank of an order under the name Marsupialia in the second edition, where they terminate that series of the Unguiculata, which possess the three kinds of teeth—incisors, canines and molars.

The hoofed animals (ungulata, 'animaux a sabots') are binarily divided into those that do, and those that do not, chew the cud; the former constituting the order Pachydermata, the latter that of Ruminantia.

The third primary group or subclass of Mammalia is indicated, but without receiving any name distinct from that of the single order Cetacea exemplifying it in the Cuvierian system—an order which would be equivalent to the Mutica of the Linnsan system, save that the manatee which Linnaeus placed in the same group as the elephant is associated with the whale in the Regne Animal.

The Mammalian system of Cuvier is exemplified in the subjoined Table:—(See p. 9).

Important as was the improvement it presented on previous classifications, the progress of anatomical and physiological knowledge, mainly stimulated by the writings and example of Cuvier himself, soon began to make felt the defects of his system. Shortly after its proposition, the zoological mind began to be disagreeably impressed by the results of the application of the characters employed by Cuvier in the formation of the primary and secondary groups of the class; the sloth, for example, being placed above the horse, the mole above the lynx, and the bat above the dog: even the Ornithorhynchus paradoxus—shewn by accurate anatomical scrutiny to be the most reptilian of the mammalian class—takes

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precedence of the colossal and sagacious elephant in the Cuvierian scheme1.

The profound admiration and respect which I have always entertained for my chief instructor in Zootomy and Zoology, never blinded me to the necessity of much modification of his arrangement of the Mammalia. The question, more especially, of the truly natural and equivalent primary groups of the class, has been present to my mind whenever I have been engaged in dissecting the rarer forms which have died at the Zoological Gardens in London, or on other occasions. But I propose first to submit to you, as briefly and clearly as I am able, the results of this store of anatomical knowledge as applicable to the true organic characters of the class Mammalia.

Mammals are distinguished outwardly by an entire or partial covering of hair2, and by having teats or mammae— whence the name of the class.

All mammals possess mammary glands and suckle their young: the embryo or foetus is developed in a womb. Their leading anatomical character is, the highly vascular and mi- Fig, i.


nutely cellular structure of the lungs, (fig. 1, I,) which are freely suspended in a thoracic cavity separated by a musculotendinous partition or 'diaphragm' from the abdomen, (ib. d.)

1 The modifications consequently proposed by Geoffroy St Hilaire, Illiger, De Blainville, C. L. Bonaparte, J. E. Gray, Waterhouse, Milne Edwards, Lesson, Wagner, Nilsson, Oken, Macleay, Sir E. Home, Gervais, and others, have been cited and commented upon in my Papers communicated to the Linnaean Society {Proceedings, 1857) and the Geological Society (Proceedings, Not. 1847, pp. 135—140).

a The foetal Cetacea shew tufts of hair on the muzzle.

Mammals, like Birds, have a heart composed of two ventricles and two auricles, and have warm blood: they breathe quickly; but inspiration is performed chiefly by the agency of the diaphragm; and the inspired air acts only on the capillaries of the pulmonary circulation.

The blood-discs are smaller than in Reptiles, and, save in the Camel-tribe, are circular in form. The right auriculoventricular valve is membranous, and the aorta bends over the left bronchial tube.

The kidneys are relatively smaller and present a more compact figure than in the other vertebrate classes; their parenchyma is divided into a cortical and medullary portion, and the secreting tubuli terminate in a dilatation of the excretory duct, called the pelvis: they derive the material of their secretion from the arterial system. Their veins are simple, commencing by minute capillaries in the parenchyma and terminating generally by a single trunk on each side in the abdominal vena cava: they never anastomose with the mesenteric veins.

The liver is generally divided into a greater number of lobes than in Birds. The portal system is formed by veins derived exclusively from the spleen and chylopoietic viscera. The cystic duct, when it exists, always joins the hepatic, and does not enter the duodenum separately. The pancreatic duct is commonly single.

The mouth is closed by soft flexible muscular lips: the upper jaw is composed of palatine, maxillary and premaxillary bones, and is fixed; the lower jaw consists of two side-halves, or rami, which are simple or formed by one bony piece, and are articulated by a convex (fig. 3, b) or flat condyle to the base of the zygomatic process, and not to the tympanic element, of the temporal bone; the base of the coronoid process (ib. c) generally extends along the space between the condyloid and the alveolar processes. The jaws of Mammals with few exceptions are provided with teeth, which are arranged in a single row; they are always lodged in sockets, and never

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