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Show TIEDDEMANN ON THE BRAIN OF THE (Ch. IV. the superiority of its intellect, because the vertical }jeight of its skull is so ~reat when compared to its horizontal length. 0 • It would be irrelevant to our subject if we were to enter Into a farther discussion on these topics, because, even if a graduated scale of organization and intelligence could have been established, it would prove nothing in favour of a tendency, in each species, to attain a higher state of perfection. We may refer the reader to the writings of Blumenbach, Prichard, Lawrence, and others, for convincing proofs that the varieties of form, colour, and organization of different races of men, are perfectly consistent with the generally received opinion, that all the individuals of the species have m·iginated from a single pair; and while they exhibit in man as many diversities of a physiological nature, as appear in any other species, they confirm also the opinion of the slight deviation from a common standard of which a species is capable. The power of existing and multiplying in every latitude, and in every variety of situation and climate, which has enabled the great human family to extend itself over the habitable globe, is partly, s~ys Lawrence, the result of physical constitution, and partly of the mental prerogative of man. If he did not possess the most enduring and flexible corporeal frame, his arts would not enable him to be the inhabitant of all climates, and to brave the extremes of heat and cold, and the other destructive influences of local situation *. Yet, notwithstanding this flexibility of bodily frame, we find no signs of indefinite departure from a common standard, and the intermarriages of individuals of the most remote varieties are not less fruitful than between those of the same tribe. There is yet another department of anatomical discovery, to which we must not omit some allusion, because it has appeared to some per ons to afford a di tant analogy, at least, to that progre ive development by which some of the inferior species may have been gradually perfected into those of more complex organization. Tieddemann found, and his discoveries have been • Lawrellce, Lectuni on Phys. Zool.andNat. Hist.ofMau1 p. 192. Ed.l823, Ch. IV.] F<ETUS IN VERTEBRATED ANIMALS. 63 most fully confirmed and elucidated by M. Serres, that the brain of the fretus, in the highest class of vertebrated animals, assumes, in succession, the various forms which belong to fishes, reptiles, and birds, before it acquires those additions and modifications which are peculiar to the mammiferous tribe. So that in the passage from the embryo to the perfect mammifer, there is a typical representation, as it were, of all those transformations which the primitive species are supposed to have under· gone, during a long series of generations, between the present period and the remotest geological era. If you examine the brain of the mammalia, says M. Serres, at an early stage of uterine life, you perceive the cerebral hemispheres consolidated, as in fishJ in two vesicles isolated one from the other ; at a later period, you see them affect the configuration of the cerebral hemispheres of reptiles ; still later again, they present you with the forms of those of birds; final1y, they acquire, at the era of bit-th, and sometimes later, the permanent forms which the adult mammalia present. The cerebral hemispheres, then, only arrive at the state which we observe in the higher animals by a series of successive metamorphoses. If we reduce the whole of these evolutions to four periods, we shall see that in the first are born the cerebral lobes of fishes, and this takes place homogeneously in all classes. The second period will give us the organization of reptiles ; the third the brain of birds ; and the fourth the complex hemispheres of mammalia. If we could develop the different parts of the brain of the inferior classes, we should make in succession a reptile out of a fish, a bird out of a reptile, and a mammiferous quadruped out of a bird. If, on the contt·~ry, we could starve this organ in the mammalia, we might reduce it successively to the condition of the brain of the three inferior classes. Nature often presents us with this last phenomenon in monsters, but never exhibits the first. Among the various deformities which organized beings may experience, they never pass the limits of their own classes to put on the forms of the class |