Page:Popular Science Monthly Volume 7.djvu/777

Rh being followed by a row of long bones, called metatarsal, attached to which are the toe-bones. Observe, further, the form and position of the heel-bone and the astragalus, the ankle-joint. Above the foot, and articulating with the astragalus, are two bones, one small (fibula), the other large (tibia). In many reptiles the ends of these bones are nearly equal. Now, in Bathmodon, a mammal from the lowest Eocene Tertiary of New Mexico and Wyoming, the tibia and fibula articulate with the astragalus and heel-bone. As in man, the fibula is the smaller, and the heel-bone is short; the animal walked on the entire sole. From Bathmodon to Horse, on the one side, and Ox on the other, there is a complete succession of intermediate forms, corresponding to succession in time. Thus in Bathmodon the astragalus is nearly flat, while in the ox its upper surface presents a grooved face of a pulley, its under surface an angulated pulley-face, and a small convexity is presented to the hollow of the heel-bone behind. The progression toward this form from Bathmodon embraces these terms: Bathmodon (a gap filled by partially-known genera), Hippopotamus, Peccary, or Oreodon, Deer, Ox. The succession of feet to the one-toed extreme, Bathmodon, Titanotherium (in the Miocene), Tapir, Horse. In the heel-bone there is a succession from the short and flat form of Bathmodon to the long and slender one of the horse and ruminants, and this increase of length is associated with elongation of the bones of the toes, and the passage from the plantigrade to the digitigrade type. Another succession is seen in the diminished number of toes. The series commences in the primitive Eocene types with five digits; in the various series leading to the horse, the ox, the hyena, the cat, the reduction proceeds by the loss of a toe from one side or the other, until, in the ruminants, but two are left, and in the horse but one. In like manner the two bones of the leg, which articulate with the foot and hand, exhibit a succession of changes.

The relation of man to this history is significant. His limbs are those of the primitive type, so common in the Eocene. He is plantigrade, has five toes, separate carpals and tarsals, short heel, flat astragalus, and neither hoofs nor claws, but something intermediate between the two. The bones of the forearm and leg are not so unequal as in the higher types, and the ankle-joint is not so perfect.

A like succession is shown to exist in the forms of the teeth; but we have not the space for even the briefest synopsis of the author's remarks on this point. Thus in limbs and in teeth man retains the characters of the primitive type. From the generalized mammalian fauna of the Eocene the carnivora developed a highly-organized apparatus for the destruction of life. The cloven-footed and odd-toed hoofed orders, are the result of constantly increasing growth of the appliances for rapid motion over the ground. The ancestors of the carnivora were developing the arts and cruelty of the chase; those of the hoofed orders were developing speed; those of the quadrumana neither speed nor weapons of defense, and nothing was left to them but arboreal life. They took to the trees, and developed the prehensile powers of the feet. In limb and tooth, and digestive system, they remain nearly in the generalized condition from which the other orders have risen. Man's prominence consists solely in the complexity and size of his brain. While the order to which he belongs has made but little progress since the Eocene, in perfecting the organization of the skeleton, it has accomplished the greatest work of all time—the evolution of the human brain and its functions. "The race has not been to the swift, nor the battle to the strong."

Muscular Structure of the Hands and Feet.—While Prof. Cope has been working on the osteology of the hand and foot, Dr. William S. Barnard has been studying their myology, or muscular structure. On the history of the muscles the fossil world can throw no light, but Dr. Barnard's investigations of living types seem to demonstrate that muscles have had a history no less significant than the bones. Prof Cope has shown that, osteologically, the human foot is of ancient pattern. What is it myologically? Let the reader attentively study his own foot; let him experiment on the toes. Try to flex them, and they move, but rather