198 AVILLIAM F. ALLEN 



mingle with the trigeminal motor root fibers, which follow along 

 the ventral surface of the trigeminal sensory root, through the 

 ventral border of the semilunar ganglion, to eventually form 

 the motor components of the nervus masticatorius, for the 

 masseter, pterygoid, and temporal muscles. None of the de- 

 scendmg mesencephalic root fibers followed the few motor fibers 

 into the mylohyoid branch of the nervus mandibularis, nor 

 entered the purely sensory divisions of the trigeminal nerve. It 

 will be seen that these results confirm May and Horsley in that 

 the descending mesencephalic root fibers enter the trigeminal 

 motor root, but disagree with them, that they end in the semi- 

 lunar ganglion. It is apparent that their studies in chroma- 

 tolysis, which were at variance and held in subjection to their 

 results from a study of Marchi preparations, were in accord with 

 my results from Marchi preparations. 



The ascending mesencephalic root fibers taking origin from 

 sensory cells in the semilunar ganglion follow along in the ventral 

 half of the trigeminal sensory root. Upon entering the pons they 

 join with the descending mesencephalic root fibers to form the 

 mesencephalic root or tract. In passing between the trigeminal 

 motor and sensory nuclei they appear to make up about one- 

 third of the mesencephalic root. Since a large number of these 

 fibers and collaterals go to the trigeminal motor nucleus, the 

 ratio of ascending to descending fibers in the mesencephalic root 

 cephalad of the trigeminal motor nucleus is reduced something 

 like 1 to 7 or 8. The number of ascending fibers continues to 

 decrease gradually as the mesencephalic root passes through the 

 inferior colliculus, until no ascending fibers were found in the 

 mesencephalic root cephalad of the trochlear nucleus. 



Without a knowledge of the character and position of the cell 

 bodies of the descending mesencephalic root fibers, it might be 

 assumed, since these fibers entered the motor root and 

 traveled in the so-called purely motor divisions of the trigeminal 

 nerve, that they were motor fibers. The writer, after making a 

 careful study of these globular unipolar mesencephalic root 

 cells, noting their position in the alar (sensory) plate, and com- 

 paring them with both the sensory cells of the semilunar gan- 



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