42 A Reconstruction of the Nuclear Masses in 



well rounded and pass into one another insensibly as soon as the great 

 increase in nuclear dimensions is attained. Slightly above the caudal pole 

 a slight concavity is made out on its ventral surface, and this is merged 

 cephalad with a slight ridge which sweeps from the middle of the ventral 

 surface laterally and cephalad. This ridge is continued superiorly as a 

 definite ventro-lateral projection of the nucleus, until it merges in the superior 

 pole. Just inferior to this ridge in the caudal half of the nucleus is a deep 

 depression on the lateral surface. Mesial to this ridge the nucleus is flattened 

 into a ventro-mesial surface, along which course the cell-columns of the 

 superior olive. Mesially, this surface insensibly blends with the mesial 

 curving face. Two marked longitudinal fissures occur in the dorsal con- 

 vexity of the nucleus. These begin slightly above the caudal pole and run 

 as fairly deep furrows, becoming more superficial as they reach more cephalic 

 regions (figure 4). 



Just cephalic to the middle of the nucleus all of these rounded surfaces 

 suddenly constrict to a considerable extent. From this point upward, the 

 nucleus, much narrowed in the two horizontal diameters, gradually tapers 

 to its sharp .sui)erior pole. This rounded caudal dilatation, with a constric- 

 tion about the middle, passing into a tapering superior extremity gives the 

 whole nucleus the appearance of a pear. 



The description just given applies to the nucleus on the left side of this 

 adult medulla. Although the nucleus on the right of this brain-stem was not 

 modeled, it was studied with the view of comparing its superior termination 

 with that on the left. The cell-mass on the left side, as modeled, shows 

 quite rapid tapering of the cephalic pole of the nucleus as compared with the 

 right. On the right, the characteristic motor cells and ground substance, 

 comprising the nucleus nervi facialis, extend cephalad as a tliin column to 

 a much higher level than on the left. This would tend to make the right 

 nucleus possess a much longer "neck" than the left and probably to be even 

 more pear-shaped. 



Attempts were made to separate the nuclear mass of the seventh nerve 

 into the various component cell-masses, described as occurring in this nucleus 

 by Van Gehuchten and Marinesco. While undoubtedly such divisions of 

 the nucleus into component parts do exist in the human medulla, the mod- 

 eling of these from the arbitrary outlines which were necessarily made to 

 determine the cell grouping was impossible. However, the occurrence of 

 the fissures and the ridge on the external surface of the nucleus is indicative 

 of such a division of the nucleus. 



NUCLEUS NERVI TRIGEMINI. 



The nucleus of the nervus trigeminus has not been modeled in its 

 entirety, as the model at its caudal cml still po.ssesses substantia gelatinosa 

 (figure 8), while at its cephalic end the main nuclear comjjlex is just devel- 

 oping (figure 14). Tliis descrii^tion, then, of the morphology of the nuclear 



