PREFACE. 



The attempt has been made in the following pages to give an 

 account of the nervous system as a whole, to trace its phylogenetic 

 history and to show the factors which have determined the course 

 of evolution. This has been made possible by recent studies 

 directed toward the analysis of the nervous system on the basis of 

 function. The functional point of view, which is the chief char- 

 acteristic of the present book, brings the treatment of the nervous 

 system into close relation with the work of recent years on the 

 behavior of animals. The study of behavior aims to give an 

 account of the actions of animals in relation to the environment. 

 The study of the nervous system aims to describe the mechanism 

 by which actions are directed and adapted to the conditions of life. 



A text-book of comparative neurology at the present time must 

 meet the needs of workers of all grades, students, investigators 

 and instructors. Its descriptions should be intelhgible to students 

 who have had one year of work in zoology or medicine, including 

 the anatomy and embryology of some vertebrate. On the other 

 hand there should be included all facts which are important for 

 the functional and phylogenetic mode of treatment. How far 

 these difficult conditions have been met only the use of the book 

 can show. Little space is given to mere descriptive anatomy and 

 some descriptive matter which is well presented in the text-books of 

 zoology, anatomy and histology in common use, is omitted. Tb''^ 

 accounts for the brief treatment of the eye, ear and other sens^ 

 organs, the distribution of the spinal nerves, etc. On the other 

 hand, every effort has been made to bring out clearly the functional 

 significance and relationships of the structures described, and to 

 interest and train the student in the interpretation of structure in 

 terms of function, adaptation and evolution. 



In the preparation of the text considerable time has been given 

 to the review of the author's earlier work and that of other writers, 

 and to the study of many unsettled questions. In this way much 



