34 A Reco7istruction of the Nuclear Masses in 



divisions of the mesial, superior, and spinal nuclei of the vestibular comjjlex. 

 Her reconstruction led to a much simpler and better idea of the vestibular 

 complex than did her earlier contribution on the subject. In this recon- 

 struction it was attempted to maintain, as far as possible, this more simple 

 conception of the vestibular complex, as is undoubtedly justified on morpho- 

 logical if not on histological grounds. The nucleus nervi vestibuli lateralis 

 has not in this study been separated from the median nucleus, as it was felt 

 that any attempt to separate this group of motor cells could only result 

 in the establishment of arbitrary lines of division. The separation of the 

 nucleus nervi vestibularis spinalis (radix descendcns) was, however, made, 

 as this division is one upon which unanimity could be secured. The nucleus 

 nervi vestibuli superior, comprising as it does the cephalic prolongation of 

 the median nucleus, shows no caudal separation from the main nuclear 

 mass. This coincides with Miss Sabin's reconstruction of the mass. As 

 far as possible the description of the whole nuclear mass will be made from 

 the standpoint of one cell-mass, but consideration will be taken of the 

 divisions of the nucleus into its well-established four chief nuclei. 



The dorsal surface of the vestibular complex lies beneath the floor of 

 the fourth ventricle in the vestibular portion of the acustic triangle (fig- 

 ure 3). It is overlaid on its caudal portion by the gray matter and fibers 

 comprising the ventricular lip of the corpus ponto-bulbare. Mesially the 

 vestibular nucleus lies in relationship to the nucleus alai cinerese (figure 11), 

 the nucleus intercalatus, the nucleus nervi abducentis, and the caudal joortion 

 of the nucleus incertus. On the dorso-lateral side of the superior half of 

 the nucleus lies the brachium conjunctivum. Laterally we find the nucleus 

 fasciculi cuneati, the corpus restiforme, and the brachium pontis, separating 

 off the nucleus nervi cochleae and the corpus ponto-bulbare. Ventrally there 

 occur the long substantia gclatinosa, the nucleus tractus solitarii. and the 

 formatio reticularis. These relationships are easily understood from inspec- 

 tion of figures 2, 3, and 4. 



The main vestibular nuclear mass, when viewed from the dorsal surface 

 (figure 3), as one passes from its caudal portion, exhibits a sudden widening 

 in the region of the middle of the nucleus, corresponding to the lateral recess 

 of the fourth ^entricle. This relationship is well shown in Miss Sabin's 

 reconstruction. Above this the main mass shows a sudden narrowing in 

 the region of the lower end of the nucleus nervi abducentis and a second, 

 just superior to this, where the fibers of the seventh nerve force the nuclear 

 material from the median line. Above this more caudal constriction, the 

 superior nucleus of the nerve may be said to lie, as it corresponds laterally to 

 the level of entrance of the nerve root and the division into ascending and 

 descending fibers. The most lateral projection of the whole nucleus repre- 

 sents the lateral collection of motor cells, comprising in part the nucleus 

 nervi vestibuli lateralis. From the cephalic j^art of the median and from 

 the superior nucleus, dorsal spurs and columns of cells lie in relationship to 



