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ART. VII.-Professor Owen on the Classification of the Mam

malia.

None of our living Naturalists displays a greater mastery over those general truths that relate to the difficult subject of classification, than Professor Owen, and we are especially indebted to him for asserting that predominance of the brain and nervous system, in indicating the real affinities of animals, which is one of the leading truths of modern Zoology. The nervous system is the primary material element in the animal, that which marks more than any other its grade of intelligence and consequent rank in nature. It is thus the basis of the animal frame; and though less obvious than the skeleton and other superadded structures, is really that which has moulded their form and proportions. No one ground of arrangement will suffice to express all those grades of relationship impressed on animals by their Maker, and perceptible by us; but some are more general and important than others; and we have long thought that the nervous system bears to the whole the relation of a grand dominant end to which all others have been bent and made subservient.

In an elaborate paper communicated to the Linnean Society, Professor Owen has applied this principle of arrangement to the mammals; and we commend the following extracts, giving a sketch of his views, to all of our readers who take an interest in Zoology.

Primary Divisions of the Mammalia.-The question or problem of the truly natural and equivalent primary groups of the class Mammalia has occupied much of my consideration, and has ever been present to my mind when gathering any new facts in the anatomy of the Mammalia, during dissections of the rarer forms which have died at the Zoological Gardens, or on other opportunities.

The peculiar value of the leading modifications of the mammalian brain, in regard to their association with concurrent modifications in other important systems of organs, was illustrated in detail in the Hunterian Course of Lectures on the Comparative Anatomy of the Nervous System, delivered by me at the Royal College of Surgeons in 1842. The ideas which were broached or suggested, during the delivery of that course, I have tested by every subsequent acquisition of anatomical knowledge, and now feel myself justified in submitting to the judgment of the Linnean Society, with a view to publication, the following fourfold primary

division of the mammalian class, based upon the four leading modifications of cerebral structure in that class.

The brain is that part of the organization which, by its superior development, distinguishes the Mammalia from all the inferior classes of VERTEBRATA; and it is that organ which I now propose to show to be the one that by its modifications marks the best and most natural primary divisions of the class.

In some mammals the cerebral hemispheres are but feebly and partially connected together by the 'fornix' and anterior commissure;' in the rest of the class a part called ' corpus callosum' is added, which completes the connecting or commissural' apparatus.

With the absence of this great superadded commissure is associated a remarkable modification of the mode of development of the offspring, which involves many other modifications; amongst which are the presence of the bones called marsupial,' and the non-development of the deciduous body concerned in the nourishment of the progeny before birth, called ' placenta;' the young in all this implacental' division being brought forth prematurely, as compared with the rest of the class.

This first and lowest primary group, or subclass, of Mammalia may be termed, from its cerebral character, Lyencephala,-signifying the comparatively loose or disconnected state of the cerebral hemispheres. The size of these hemispheres (fig. 1, A) is such that they leave exposed the olfactory ganglions (a), the cerebellum (c), and more or less of the optic lobes (B); their surface is generally smooth; the anfractuosities, when present, are few and simple.

The next well-marked stage in the development of the brain is where the corpus callosum (indicated in fig. 2, by the dotted lines d, d) is present, but connects cerebral hemispheres as little advanced in bulk or outward character as in the preceding subclass; the cerebrum (A) leaving both the olfactory lobes (a) and cerebellum (c) exposed, and being commonly smooth, or with few and simple convolutions in a very small proportion, composed of the largest members of the group. The mammals so characterized constitute the subclass Lissencephala, (fig. 2).

In this subclass the testes are either permanently or temporarily concealed in the abdomen: there is a common external genitou inary aperture in most; two precaval veins ('superior' or 'anterior venæ ') terminate in the right auricle. The squamosal in many, retain their primitive separation as distinct bones. The

orbits have not an entire rim of bone. Besides these more general characters by which the Lissencephala, in common with the Lyencephala, resemble Birds and Reptiles, there are many other remarkable indications of their affinity to the Oviparous Vertebrata in particular orders or genera of the subclass. Such, e. g., are the cloaca, convoluted trachea, supernumerary cervical vertebræ and their floating ribs, in the 3-toed Sloth; the irritability of the muscular fibre, and persistence of contractile power in the Sloths and some other Bruta; the long, slender, beak-like edentulous jaws and gizzard of the Anteaters; the imbricated scales of the equally edentulous Pangolins, which have both gizzard and gastric glands like the proventricular ones in birds; the derma bony armour of the Armadillos like that of loricated Saurians; the qui ls of the Porcupine and Hedgehog; the proventriculus of the Dormouse and Beaver; the prevalence of disproportionate development of the hind-limbs in the Rodentia; coupled, in the Jerboa, with confluence of the three chief metatarsals into one bone, as in birds; the keeled sternum and wings of the Ba's; the aptitude of the Cheiroptera, Insectivora, and certain Rodentia to fall, like Reptiles, into a state of true torpidity, associated with a corresponding faculty of the heart to circulate carbonized or black blood-these, and the like indications of co-affinity with the Lyencephala to the Oviparous air-breathing Vertebrata, have mainly prevailed with me against an acquiescence in the elevation of different groups of the Lissencephala to a higher place in the Mammalian series, and in their respective association, through some single character, with better-brained orders, according to Mammalogical systems which, at different times, have been proposed by zoologists of deserved reputation. Such, e.g., as the association of the long-clawed Bruta with the Ungulata, and of the shorter-clawed Shrews, Moles and Hedgehogs, as well as the Bats, with the Carnivora; of the Sloths with the Quadrumana; of the Bats with the same high order; and of the Insectivora and Rodentia in immediate sequence after the Linnean Primates,' as in the latest published System of Mammalogy,' from a distinguished French author.

The third leading modification of the Mammalian cerebrum ist such an increase in its relative size, that it extends over more or less of the cerebellum; and generally more or less over the olfac tory lobes. Save in very few exceptional cases of the smaller and inferior forms of Quadrumana (fig. 3) the superficies is folded into more or less numerous gyri or convolutions,-whence the

name Gyrencephala, which I propose for the third subclass of Mammalia (fig. 4.)

In this subclass we shall look in vain for those marks of affinity to the Ovipara, which have been instanced in the preceding subclasses. The testes are, indeed concealed, and through an obvious adaptive principle, in the Cetacea; but, in the rest of the subclass, with the exception of the Elephants, they pass out of the abdomen, and the Gyrencephalous quadrupeds, as a general rule, have a scrotum. The vulva is externally distinct from the anus. With the exception, again, of the Elephants, the blood from the head and anterior limbs is returned to the right auricle by a single precaval trunk. The mammalian modification of the Vertebrate type attains its highest physical perfection in the Gyrencephala, as manifested by the bulk of some, by the destructive mastery of others, by the address and agility of a third order. And, through the superior psychological faculties an adaptive intelligence pre dominating over blind instinct-which are associated with the higher development of the brain, the Gyrencephala afford those species which have ever formed the most cherished companions and servitors, and the most valuable sources of wealth and power, to Mankind.

In Man the brain presents an ascensive step in development, higher and more strongly marked than that by which the preceding subclass was distinguised from the one below it. Not only do the cerebral hemispheres (figs. 5 & 6, A) overlap the olfactory lobes and cerebellum, but they extend in advance of the one, and further back than the other (fig. 6, c). Their posterior develop ment is so marked, that anatomists have assigned to that part the character of a third lobe; it is peculiar to the genus Homo and equally peculiar is the posterior horn of the lateral ventricle,' and the hippocampus minor,' which characterize the hind lobe of each hemisphere. The superficial grey matter of the cerebrum, through the number and depth of the convolutions, attains its maximum of extent in Man.

Peculiar mental powers are associated with this highest form of brain, and their consequences wonderfully illustrate the value of the cerebral character; according to my estimate of which, I am led to regard the genus Homo, as not merely a representative of a distinct order, but of a distinct subclass of the Mammalia, for which I propose the name of Archencephala,' (fig. 6).

Prosessor Owen then proceeds to subdivide his primary groups into orders. We can only give extracts bearing upon groups of special interest.

LYENCEPHALA.

In the Lyencephalous Mammalia some have the optic lobe' simple, others partly subdivided, or complicated by accessory ganglions, whence they are called 'bigeminal bodies.' The Lycene phala with simple optic lobes are edentulous' or without calcified teeth, are devoid of external ears, scrotum, nipples, and marsupial pouch they are true testiconda;' they bave a coracoid bone extending from the scapula to the sternum, and also an epicoracoid and episternum, as in Lizards; they are unguiculate and pentadactyle, with a supplementary tarsal bone supporting a perforated spur in the male. The order so characterized is called 'MONOTREMATA,' in reference to the single excretory and generative outlet, which, however, is by no means peculiar to them among Mammalia. The Monotremes are insectivorous, and are strictly limited to Australia and Tasmania.

The MARSUPIALIA are Mammals distinguished by a peculiar pouch or duplicature of the abdominal integument, which in the males is everted, forming a pendulous bag containing the testes; and in the females is inverted, forming a hidden pouch containing the nipples and usually sheltering the young for a certain period after their birth: they have the marsupial bones in common with the Monotremes ; a much-varied dentition, especially as regards number of incisors, but usually including 4 true molars; and never more than 3 premolars the angle of the lower jaw is more or less inverted.

With the exception of one genus, Didelphys, which is American, and another genus Cuscus, which is Malayan, all the known existing Marsupials belong to Australia, Tasmania, and New Guinea. The grazing and browsing Kangaroos are rarely seen abroad in full daylight, save in dark rainy weather. Most of the Marsupialia are nocturnal. Zoological wanderers in Australia, viewing its plains and scanning its scrubs by broad daylight, are struck by the seeming absence of mammalian life; but during the brief twilight and dawn, or by the light of the moon, numerous forms are seen to emerge from their hiding-places and illustrate the variety of marsupial life with which many parts of the continent abound. We may associate with their low position in the mammalian scale the prevalent habit amongst the Marsupialia of limiting the exercise of the faculties of active life to the period when they are shielded by the obscurity of night.

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