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stegosaurus, the remains of which have also been found in the Western Jurassic and are preserved at the Yale College Museum. It was about twenty-five feet long. Its skull contained a brain which is comparatively the smallest brain which we know in any quadruped. It was, indeed, so small that it was probably not sufficient to control and direct all the nerves and muscles of the gigantic body. At any rate, we find in the stegosaurus that the vertebrae of the sacrum contain a cavity formed by an enlargement of the spinal canal. This chamber is ovate in form, and resembles the brain-case in the skull, but it is very much larger, being at least ten times the size of the cavity of the brain. Although we find in some animals a swelling of the spinal cord at the same place, there is nothing known which might be put beside the stegosaurus in this respect, and it is difficult to object if somebody claims that the animal possessed two brains—one in his skull and the other in his sacrum. The stegosaurus was, according to Marsh, protected and armed in the following way: At the region of the throat and low-er part of the neck there were small dermal plates in the thick skin, which were regularly arranged. The upper part of the neck was shielded by larger plates of the same kind, which were placed in pairs on each side. These plates of bone increased in size posteriorly, and covered the back. From the sacrum