PREFACE xi 



In addition to these microscopic studies, reconstructions according to 

 the Bourne method have been employed. Such reconstructions, made at a 

 magnification of lo or 12 diameters, reveal the intimate characters and 

 dmiensional relations of the gray matter. By no other means is it possible 

 to acquire so comprehensive a conception of the complex nature of the 

 internal structure in the brain stem. Dr. Riley has devoted himself to this 

 \\()rk for a number of years and as a result has produced a series of most 

 illuminating reconstruction models which present this aspect of the subject 

 so as to disclose beyond all question the major nuclear movements in the 

 evolutionary process of the primate brain. I am indebted to Dr. Riley not 

 merely for the production of this collection of unsurpassed models, but 

 equally for the careful descriptions which he has given of them in the eleven 

 chapters dealing with this phase of the subject. 



For the purpose of further checking the proportional relations of the 

 various structures m the brain stem, several methods of mensuration have 

 been employed. On the basis of these measurements, two series of coefTicients 

 were established: first, planimctric coefficients in which the transverse 

 proportions of a given structure were estimated in relation to the entire 

 cross section by means of a planimeter. This method produced a series of 

 figures which afford a basis of metric comparison of homologous structures. 

 For the painstaking work in these protracted planimetric calculations I am 

 indebted to Mrs. Seymour Basch, whose repeated measurements and remeas- 

 urements of each structure required the most exacting application and 

 produced results which are probably as close an approximation to actual 

 facts as may be obtained. Second, estimates for longitudinal coefficients were 

 made with the purpose of determining the relative length of each structure 

 to the entire length of the brain stem. 



While it is probably true that no method of mensuration may express 

 adequately the relative proportions of the several structures considered 



