476 DAVIDSON BLACK 
this connection reference should be made to the exact nuclear 
reconstructions made by Berkelbach Van der Sprenkel and to 
the discussion by this author of the method he employed (92). 
In not a few instances, nuclear masses other than those of the 
motor nerves have been plotted on the charts. This has been 
done, for example, in the case of the superior olive and inferior 
olive (nucleus paramedianus) in such forms as they occur in a 
sufficiently well differentiated condition to allow a sharp de- 
marcation. Similarly the site of the tip of the calamus scrip- 
torius is indicated in all forms with the exception of myxinoids, 
where a true calamus is absent. The addition of these land- 
marks has been made to facilitate the comparison of different 
forms one with another by increasing the number of points for 
comparison. 
Fig. 7 Reconstruction charts of motor roots and nuclei: (A), Petromyzon 
fluviatilis (after Kappers, 66). (B), Myxine glutinosa (after! Rothig and Kap- 
pets, 88). (C), Bdellostoma dombeyi. Explanation of signs and abbreviations 
used in all charts as follows: V/., abducens root; /X., motor glossopharyngeal 
root; X., motor vagus rootlets; Sp.occ., motor spino-occipital rootlets. The 
arrow indicates the site of the calamus. 
= Oculomotor root and nucleus 
HUTT Trochlear root and nucleus 
Trigeminus motor root and nucleus 
SEO Abducens nucleus 
Facial motor root and nucleus 
Glossopharyngeus motor nucleus 
YL Vagus motor nucleus 
BEY Spino-occipital motor roots and nucleus 
a Nu.olivaris superior 
Nu.paramedianus 
