In the Museum at Heidelberg a skull of this kind is seen in the long-tailed genus of Pterodactyles named Rhamphorhynchus. It shows the large rounded cerebral hemispheres, which extend in front of cerebral masses of smaller size a little below them in position, which perhaps are as like the brain of a monotreme mammal as a bird. The short-tailed Pterodactylus described by Cuvier has the cerebral hemispheres very similar to those of a bird, but the relations of the hinder parts of the brain to each other are less clear. The first specimen to show the back of the brain was found by Mr. John Francis Walker, M.A., in the Cambridge Greensand. I was able to remove the thick covering of cellular bone which originally extended above it, and thus expose evidence that in the mutual relations of the fore and hind parts of the brain bird and ornithosaur were practically identical. Another Cambridge Greensand skull showed that in the genus Ornithocheirus the optic lobes of the brain are developed laterally, as in birds. That skull was isolated and imperfect. But about the same time the late Rev. W. Fox, of Brixton, in the Isle of Wight, obtained from Wealden beds another skull, with jaws, teeth, and the principal bones of the skeleton, which showed that the Wealden Pterodactyle Ornithodesmus had a similar and bird-like brain. In 1888 Mr. E. T. Newton, F.R.S., obtained a skull from the Upper Lias, uncrushed and free from distortion. This made known the natural mould of the brain, which shows the cerebral hemispheres, optic lobes, and cerebellum more distinctly than in the specimens previously known. In some respects it recalls the Heidelberg brain of Rhamphorhynchus in the apparently transverse subdivision of the optic lobes, but it is unmistakably bird-like, and quite unlike any reptile. IMPORTANCE OF THE BRAIN AND BREATHING ORGANS