18 bulletin: museum of comparative zoology. 



U. Spinal nerves 93 



1. Third spinal nerve 93 



2. Second spinal nerve ....... 95 



3. First spinal nerve ........ 95 



4. Connections of first three spinal nerves with sympathetic. 95 

 V. General considerations on nerve XII and the spinal nerves . . 96 



W. General summary 98 



Bibliography 101 



Explanation of plates 109 



A. INTRODUCTION. 



It is now generally recognized that the comparative anatomy of the 

 nervous system can not be profitably studied without recoui'se to 

 microscopic analysis in the peripheral region as well as in the central 

 organs. It is further recognized that, for their final explanation, the 

 highly complex nervous organs of mammals, including man, must 

 await the revisions and additions which such a method of study, 

 applied to the lower vertebrates, will suggest for their interpretation. 

 Inasmuch as the nervous system is essentially a correlating structure, 

 it follows naturally that changes in its mechanism should be studied 

 in connection with a study of the correlated organs and functions. 

 This gives to the study of the nervous system a broader biological 

 significance than is possessed by other organs. But this relation adds 

 much to the technical difficulties and makes it almost impossible to 

 bring within the scope of a single research the complete analysis of 

 even a single form. The shortcomings of the present study from that 

 point of view are recognized by the author. However, in the methods 

 pursued, he has had constantly in mind the larger problem, which 

 does not recognize the arbitrary distinction between central and pe- 

 ripheral nervous systems. In fact, he has already collected much 

 material and information on the central nervous system of Anolis; 

 but it seems advisable to reserve that material for a more complete 

 account of the Anolis brain. The present investigation is carried far 

 enough toward the nerve centers to articulate easily with such a study. 



A large part of this work was done a number of years ago in the 

 Zoological Laboratory of Harvard University. Since then it has been 

 continued in the Laboratory of Histology and Embryology of the 

 University of Nebraska, College of Medicine. In this connection I 

 wish to acknowledge my gratitude to Dr. E. L. Mark for placing every 



