THE ACOUSTIC COMPLEX OF THE OPOSSUM 403 



50 microns and stained by the Weigert-Pal method. Two addi- 

 tional transverse series which were prepared by Dr. McCotter 

 and Dr. Kollig, later became available for comparison. 



In preparing the reconstructions the Born wax-plate technique 

 has been followed with slight modification. The drawings were 

 made with the projection lantern and corrected from the sections 

 with the binocular microscope. The sheets were incorporated in 

 millimeter plates, the selected structures being then cut out and 

 piled. Models were made from sections in all three planes, and 

 each used as a check upon the other. After making some pre- 

 Uminary models it was found that the best results on the whole 

 were obtained from the transverse sections. Two finished models 

 from this set were accordingly made, and it is from these that the 

 illustrations for this paper are taken. Of the two models, one 

 was made with the parts rigid, the restiform body, the pons and 

 the brachium conjunctivum being included together with the 

 seventh nerve as landmarks. The other is a dissectible model 

 including nothing but the cochlear and vestibular complexes and 

 the seventh nerve. It was found possible to so construct this 

 model that the separate groups could be shown independently. 

 From it the drawings of the two individual systems were made. 

 Reconstruction was carried anteriorly only far enough to include 

 most of the corpus geniculatum mediale. The course of the audi- 

 tory path anterior to this point was found to be too indefinitely 

 defined to permit of satisfactory rendition by this method. The 

 relation of the superior nucleus of the vestibular to the floor of 

 the cerebellum and its basal nuclei was also rather baffling. In 

 such cases as the latter, where the models do not clearly show the 

 points involved, resort has been made to drawings of the sections 

 themselves, which it is hoped will aid the reader in following the 

 text. 



It has become increasingly evident to the writer as this study 

 has progressed that the approaching of the problem from the 

 standpoint of finer histological detail, as obtained by the Golgi 

 and Cajal silver reduction methods, would be essential to the 

 reaching of conclusive results on many of the points of anatomical 

 structure mentioned in this paper. Although a Golgi series is 



