PREFACE 



THIS work reports the results of a search, extending over fifty 

 years, for the fundamental plan of the vertebrate nervous sys- 

 tem as revealed in generalized form in the amphibians. In these small 

 brains we find a simplified arrangement of nerve cells and fibers 

 with a pattern of structural organization, the main features of which 

 are common to all vertebrates. From this primitive and relatively 

 unspecialized web of tissue it is possible to follow the successive 

 steps in progressive elaboration as the series of animals from sala- 

 manders to men is passed in review. 



This is a record of personal observation, not a compilation of the 

 literature. It is presented in two parts, which differ in content and 

 method of treatment of the data. 



The first part gives a general over-all view of the structure without 

 details, followed by physiological interpretation and discussion of 

 some general principles of embryologic and phylogenetic mor- 

 phogenesis. This part, with the accompanying illustrations, can be 

 read independently of the histological details recorded in the second 

 part. 



The second part presents the evidence upon which conclusions are 

 based, drawn from my own previously published descriptions, to 

 which references are given, together with considerable new material. 

 This part is designed for specialists in comparative neurology and as a 

 guide for physiological experiments. The second part supplements the 

 first, to which the reader must make frequent reference. 



Grateful acknowledgment is made to many colleagues for generous 

 assistance and criticism, and particularly to Doctors Elizabeth C. 

 Crosby, Davenport Hooker, Olof Larsell, Gerhardt von Bonin, 

 Ernst Scharrer, and W. T. Dempster. In the preparation of the man- 

 uscript invaluable help was given by Miss Anna Seaburg. 



I am indebted to Dr. Paul G. Roofe for permission to copy one of 

 his pictures, shown here as figure 86A. The American Museum of 

 Natural History, New York, generously furnished the two photo- 

 graphs, taken from life, shown at the bottom of the Frontispiece. 

 These are copyrighted by the Museum. One of them has been pre- 

 viously published by the Macmillan Company in Hegner's Parade 



