In the following pages the term skeleton is used in its widest sense, so as to include exoskeletal or tegumentary structures, as well as endoskeletal structures. It was thought advisable to include some account of the skeleton of the lowest Chordata—animals which are not strictly vertebrates, but it seemed undesirable to alter the title of the book in consequence.

The plan adopted in the treatment of each group has been to give first an account of the general skeletal characters of the group in question and of its several subdivisions; secondly to describe in detail the skeleton of one or more selected types; and thirdly to treat the skeleton as developed in the group organ by organ.

A beginner is advised to commence, not with the introductory chapter, but with the skeleton of the Dogfish, then to pass to the skeletons of the Newt and Frog, and then to that of the Dog. After that he might pass to the introductory chapter and work straight through the book. I have endeavoured to make the account of each type skeleton complete in itself; this has necessitated a certain amount of repetition,—a fault that I have found it equally difficult to avoid in other parts of the book.

Throughout the book generic names are printed in italics; and italics are used in the accounts of the type skeletons for the names of membrane bones. Clarendon type is used to emphasise certain words. In the classificatory table the names of extinct genera only, are printed in italics.

In a book in which an attempt is made to cover to some extent such a vast field, it would be vain to hope to have avoided many errors both of omission and commission, and I owe it to the kindness of several friends that the errors are not much more numerous. I cannot however too emphatically say that for those which remain I alone am responsible. Messrs C.W. Andrews, E. Fawcett, S.F. Harmer, J. Graham Kerr, and B. Rogers have all been kind enough to help me by reading proofs or manuscript, while the assistance that I have received from Dr Gadow during the earlier stages and from Prof. Lloyd Morgan and Mr Shipley throughout the whole progress of the work has been very great. To all these gentlemen my best thanks are tendered.

All the figures except 1, 35, 55, and 84 were drawn by Mr Edwin Wilson, to whose care and skill I am much indebted. The majority are from photographs taken by my sister Miss K.M. Reynolds or by myself in the British Museum and in the Cambridge University Museum of Zoology, and I take this opportunity of thanking Sir W.H. Flower and Mr S.F. Harmer for the facilities they have afforded and for permission to figure many objects in the museums respectively under their charge. I have also to thank (1) Prof. von Zittel for permission to reproduce figs. 27, 41, 52, 69, 70, 80, 106 A, and 107 C; (2) Sir W.H. Flower and Messrs A. and C. Black for figs. 1 and 84; (3) Prof. O.C. Marsh and Dr H. Woodward for fig. 35; (4) Dr C.H. Hurst and Messrs Smith, Elder, and Co. for fig. 55.

A few references are given, but no attempt has been made to give anything like a complete list. The abbreviations of the titles of periodicals are those used in the Zoological Record.

I have always referred freely to the textbooks treating of the subjects dealt with, and in particular I should like to mention that the section devoted to the skeleton of mammals is, as it could hardly fail to be, to a considerable extent based on Sir W.H. Flower's Osteology of the Mammalia.

SIDNEY H. REYNOLDS.

March 10, 1897.