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Updated: June 18, 2025
The Placental Mammals were the best equipped of all the life-forms for survival and development, for the reason that the young were nourished during their critical period, and the care that the mammal must of necessity give to her young operated in the direction of affording a special protection far superior to that of the other forms.
This and other causes acted to place the Placentals in the "Royal line" from which Man was evolved. The following families of Placental Mammals are recognized by Science, each having its own structural peculiarities: The Edentata, or Toothless creatures, among which are the sloths, ant-eaters, armadillos, etc. These animals seem to be closer to the Monotremes than they are to the Marsupials;
We should all, at once, agree upon placing him among the mammalian vertebrates; and his lower jaw, his molars, and his brain, would leave no room for doubting the systematic position of the new genus among those mammals, whose young are nourished during gestation by means of a placenta, or what are called the 'placental mammals.
They have 1, A vertebral column; 2, Mammae; 3, A placental embryo; 4, Four legs; 5, A single well-developed toe in each foot provided with a hoof; 6, A bushy tail; and 7, Callosities on the inner sides of both the fore and the hind legs.
A step higher in the scale, among the placental Mammals, the structure of the brain acquires a vast modification not that it appears much altered externally, in a Rat or in a Rabbit, from what it is in a Marsupial nor that the proportions of its parts are much changed, but an apparently new structure is found between the cerebral hemispheres, connecting them together, as what is called the 'great commissure' or 'corpus callosum. The subject requires careful re-investigation, but if the currently received statements are correct, the appearance of the 'corpus callosum' in the placental mammals is the greatest and most sudden modification exhibited by the brain in the whole series of vertebrated animals it is the greatest leap anywhere made by Nature in her brain work.
In Denmark it was believed that if a woman were to creep through a colt's placental membrane stretched between four sticks, she would for the rest of her life bring forth children without pain or illness; but all the boys would in such case be werewolves, and all the girls Maras, or nightmares.
The preoccupancy of the country by such indigenous tribes may have checked the development of the placental Rodents and Cheiroptera, even were we to concede the possibility of such forms being convertible by variation and progressive development into higher grades of mammalia.
Amongst other points Professor Huxley called attention to the resemblance between the anterior molars of the placental dog with those of the marsupial thylacine. These, indeed, are strikingly similar, but there are better examples still of this sort of coincidence. Thus it has often been remarked that the insectivorous marsupials, e.g.
In the case of a syphilitic mother it is most probable that the infection is conveyed to the fœtus by the placental circulation. In the case of a syphilitic father, it is commonly believed that the infection is conveyed to the ovum through the seminal fluid at the moment of conception.
We should all, at once, agree upon placing him among the mammalian vertebrates; and his lower jaw, his molars, and his brain, would leave no room for doubting the systematic position of the new genus among those mammals, whose young are nourished during gestation by means of a placenta, or what are called the 'placental mammals.
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