402 JOHN H. STOKES 



In carrying on the present study, the basic work of Held upon 

 the central acoustic path has been constantly referred to ; likewise 

 the studies of Cajal and v. Kolliker and the compilation of results 

 given in Barker's text. From the standpoint of reconstruction 

 the work of Sabin upon the medulla of the new-born child has 

 been applied wherever possible as a guide to the region under 

 consideration. The reconstruction work of Streeter upon the 

 cranial nerves and upon the embryology of the peripheral audi- 

 tory apparatus, that of Essick upon the corpus ponto-bulbare, 

 and the as yet unpublished work carried on in this laboratory 

 by Calhoun upon the cranial nerves of the opossum other than the 

 eighth, have been similarly employed. 



As regards the investigation of the brain in Monotremes and 

 Marsupials, the publications of G. Eliott Smith and the work 

 of Ziehen, require mention. Their studies, however, did not 

 extend to the fiber-paths of the hindbrain. Published work on 

 the opossum brain itself has been confined apparently to a paper 

 by Herrick on the olfactory apparatus, giving a brief description 

 and a few typical sections of the region studied. The immediate 

 field of this paper is therefore comparatively virgin. In fact the 

 central acoustic apparatus considered alone, has never been the 

 subject of three-dimensional reconstruction purely for its own 

 sake — so that it is hoped that in this direction the present study 

 will prove a serviceable aid in the visualization and comprehen- 

 sion of this important division of the central nervous system. 



It may be stated at this point that the study of the seventh 

 nerve that appears in the reconstructions, is incidental. Morpho- 

 logically its relations to the eighth makes it a valuable landmark, 

 and it is largely for its value in this direction that it was included 

 in the modelling. 



MATERIAL AND METHODS 



The material upon which the study was carried out consists 

 of three sets of serial sections, in the transverse, sagittal and 

 horizontal planes respectively, of the entire brain of the adult 

 opossum. These sections are the property of this laboratory and 

 were prepared by Dr. R. R. Pinckard. The sections were cut at 



