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Page:Popular Science Monthly Volume 32.djvu/511

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AMERICAN ZOÖLOGISTS AND EVOLUTION.

Dr. Spencer Trotter[1] has made a study of the collar-bone and its significance, in which he accounts for its presence or absence in mammalia by correlating it with the life-habits of the animal in the use of the fore-limb. He says: "Every fully-developed tissue in an organism is needed, or it would not be there; and just so soon as by increasing change in life and habits it becomes a factor of less and less importance to the animal, it fails more and more to attain its former standard of development, and in time falls back to the primitive condition from which it arose and finally disappears."

Many new and interesting facts have been added sustaining the affinity between the birds and reptiles. Professor O. C. Marsh[2] made a careful study of the Archæopteryx in the British Museum. The new points he has added bring out still more strongly the extraordinary characters blended in this creature. Among other features he discovered the separate condition of the pelvic bones, and shows that while it must be considered a bird, yet it has true teeth, bi-concave vertebræ, three separate fingers in each hand, all furnished with claws, metatarsals and metacarpals, equally unanchylosed and the pelvic bones separate, as already mentioned.

Dr. J. Amory Jeffries,[3] in the study of the claws and spurs on birds' wings, has presented an interesting table showing the number of phalanges in each finger, from the highest to the lowest family of birds, with the presence or absence of claws recorded for each finger. This table shows very clearly that the higher birds have fewer phalanges and no claws, and as one approaches the lower families the phalanges increase in number, the first finger having two phalanges, and the second and third fingers being tipped with claws.

In a brief study of the tarsus of low aquatic birds,[4] made with special reference to the interpretation of the ascending process of the astragalus with the intermedium of reptiles, I observed a separate center of ossification for this so-called process, observed its unquestionable position between the tibiale and fibulare, its increase in size with the growth of the bird, and its final anchylosis with the proximal tarsal bones. In the bones of a young Dinornis, which through the courtesy of Dr. Henry Woodward I was kindly permitted to examine in the British Museum, the ascending process was large and conspicuous and firmly anchylosed with the coössified tarsals to the distal end of the tibia. Professor Marsh,[5] in a study of the metartasal bones of Ceratosaurus, a Dinosaur discovered by him, found that the metatarsals coössified in the same manner as those of the penguin.

The question as to the existence of a sternum in Dinosaurian

  1. "American Naturalist," vol. xix, p. 1172.
  2. "American Journal of Science and Arts," vol. xxii, p. 338.
  3. "Proceedings of the British Society of Natural History," vol. xxi, p. 301.
  4. "Anniversary Memoirs of the British Society of Natural History," 1880.
  5. "American Journal of Science and Arts," vol. xxvlii, p. 161.