Page:Popular Science Monthly Volume 20.djvu/328

From Wikisource
Jump to navigation Jump to search
This page has been validated.
314
THE POPULAR SCIENCE MONTHLY.

One of the most interesting points determined during my investigation of Archæopteryx was the separate condition of the pelvic bones. In all other known adult birds, recent and extinct, the three pelvic elements, ilium, ischium, and pubis, are firmly anchylosed. In young birds these bones are separate, and in all known Dinosaurian reptiles they are also distinct. This point may, perhaps, be made clearer by referring to the two diagrams before you, which I owe to the kindness of my friend Dr. Woodward, of the British Museum, who also gave me excellent facilities for examining the Archæopteryx under his care. In the first diagram, we have represented the pelvis of an American Jurassic Dinosaur allied to Iguanodon, and here the pelvic bones are distinct. The second diagram is an enlarged view of the pelvis of the Archæopteryx in the British Museum, and here too the ilium is seen separate from the ischium and pubis.

In birds the fibula is usually incomplete below, but it may be co-ossified with the side of the tibia. In the typical Dinosaurs, Iguanodon, for example, the fibula at its distal end stands in front of the tibia, and this is exactly its position in Archæopteryx, an interesting point not before seen in birds.

The metatarsal bones of Archæopteryx show, on the outer face at least, deep grooves between the three elements, which imply that the latter are distinct, or unite late together. The free metacarpal and separate pelvic bones would also suggest distinct metatarsals, although they naturally would be placed closely together, so as to appear connate.

Among other points of interest in Archæopteryx may be mentioned the brain-cast, which shows that the brain, although comparatively small, was like that of a bird, and not that of a Dinosaurian reptile. It resembles in form the brain-cast of Laopteryx, an American Jurassic bird, which I have recently described. The brain of both these birds appears to have been of a somewhat higher grade than that of Hesperornis, but this may have been due to the fact that the latter was an aquatic form, while the Jurassic species were land birds.

As the Dinosauria are now generally considered the nearest allies to birds, it was interesting to find, in those investigated, many points of resemblance to the latter class. Compsognathus, for example, shows in its extremities a striking similarity to Archæopteryx. The three clawed digits of the manus correspond closely with those of that genus; although the bones are of different proportions. The hind-feet also have essentially the same structure in both. The vertebræ, however, and the pelvic bones of Compsognathus differ materially from those of Archæopteryx, and the two forms are in reality widely separated. While examining the Compsognathus skeleton, I detected in the abdominal cavity the remains of a small reptile which had not been previously observed. The size and position of this in-