The extinct Pterodactyles hold a relation to Birds in the scheme of life not unlike that which Monotremata hold to other Mammals. Both are remarkable for the variety of their affinities and resemblances to Reptiles. The Ornithosauria have long passed away; the Monotremes are nearing extinction. Both appear to be supplanted by parallel groups which were their contemporaries. Birds now fill the earth in a way that Flying Reptiles never surpassed; but their flight is made in a different manner, and the wing is extended to support the animal in the air, chiefly by appendages to the skin. If these fossils have taught that Ornithosaurs have a community of soft vital organs with Dinosaurs and Birds, they have also gone some way towards proving that causes similar to those which determined the structural peculiarities of their bony framework, originated the special forms of respiratory organs and brain which lifted them out of association with existing Reptiles. These old flying animals sleep through geological ages, not without honour, for the study of their story has illuminated the mode of origin of animals which survive them, and in cleaving the rocks to display their bones we have opened a new page of the book of life. APPENDIX The best public collections of Ornithosaurian remains in England are in the British Museum (Natural History); Museum of Practical Geology, Royal College of Surgeons; the University Museum, Oxford; Geological Museum, Cambridge; and the Museum of the Philosophical Society at York. Detailed descriptions and original figures of the principal specimens mentioned or referred to may be found in the following writings:-- H. v. Meyer, _Reptilien aus dem Lithograph_. _Schiefer_. 1859. Folio. v. Quenstedt, _Pterodactylus suevicus_. 1855. 4to. Goldfuss, _Nova Acta Leopold_. XV. v. Munster, _Nova Acta Leopold_. XV. A. Wagner, _Abhandl. Bayerischen Akad._, vi., viii. Cuvier, _Annales du Museum_, xiii. 1809. " _Ossemens fossiles_, v. 1824. Buckland, _Geol. Trans._, ser. 2, iii. R. Owen, _Palæontographical Society_. 1851, 1859, 1860, 1870, 1874. K. v. Zittel, _Palæontographica_, xxix. 1882. T. C. Winkler, _Mus. Teyler Archives_. 1874, 1883. Oscar Fraas, _Palæontographica_, xxv. 1878. Anton Fritsch, _Böhm. Gesell. Sitzber_. 1881. R. Lydekker, _Catalogue of Fossil Reptilia in British Museum_ I. 1888. O. C. Marsh, _Amer. Jour. Science_. 1882, 1884. S. W. Williston, _Kansas University Quarterly_. 1893, 1896. E. T. Newton, _Phil. Trans. Royal Soc._ 1888, 1894. H. G. Seeley, _Ornithosauria_. 8vo. 1870. " _Annals and Mag. Natural Hist._ 1870, 1871, 1890, 1891. " _Linn. Society_. 1874, 1875. " _Geol. Mag._ 1881. Felix Pleininger, _Palæontographica_. 1894, 1901. INDEX A Abdominal ribs, 85, 154 Accumulation of characters, 220 Acetabulum, 95 Acquired characters, 219 Adjacent land, 136 Air cells, 10, 48 Albatross, 23, 36, 176