The Journal of 



Comparative Neurology and Psychology 



Volume XIX December, 1909 - Number 6 



THE RADIX MESENCEPHALICA TRIGEMINL^ 



BY 



J. B. JOHNSTON. 

 With Thirty-two Figures. 



The first author to correctly describe the midbrain or ''descending" 

 root of the trigeminus was Mejnert. In his chapter on the brain of 

 mammals contributed to Strieker's Handbuch der Lehre von den 

 Geweben, he describes the root in the following manner: "'This root 

 descends along the outer side of the central, tubular gray matter of 

 the aqueduct, and passes onward through the region of the pons, in 

 the meantime constantly increasing in bulk, and buried in the lateral 

 region of the gray floor of the ventricle that lies along the inner surface 

 of the processus cerebelli ad cerebrum. It presents on cross-sections 

 a semi-lunar surface, which Stilling and Deiters took for an ascend- 

 ing trochlearis-root, and along its inner border lie, through a large 

 part of its course, the clusters of cells from which the fibers of the 

 root spring, so disposed as to remind one of grape clusters. These 

 cells are distinguished from those of the substantia ferruginea by the 

 roundness of their form, and by their containing no pigment" (Ameri- 

 can edition, p. 7-jo). He does not discuss the possibility of the root 

 being motor in character, but simply describes it as one of the primary 



^Neurological Studies from the Institute of Anatomy. University of Minne- 

 sota, No. 8. 



The .Journal of CoMrARATivE XEinoLuOY axd rsYcnoLooY. — Vol. XIX, No. 0. 



