170 WILLIAM F. ALLEN 



was more or less spherical in shape, extending from in front of the 

 mferior olive to the nucleus of the oculomotor nerve. Serial 

 sections of the bram, after a modified Marchi treatment,^ 

 demonstrated that the center of the tumor was in the neighbor- 

 hood of a section through the trigeminal motor nucleus. Here 

 the tumor had pushed up a narrow strip of the brain substance 

 into the fourth ventricle. So far as could be determined, it had 

 not severed the mesencephalic root fibers, but had injured all of 

 the trigeminal root fibers on each side, in their course through 

 the brachium pontis. In the region of the trochlear nucleus, or 

 a little caudal (fig. 1), the tumor still occupies a large part of the 

 pons and had pushed a narrow strip of the brain substance up 

 into the aquaeductus cerebri (Sylvii), but apparently had not 

 destroyed the trochlear nucleus nor the cells and fibers of the 

 mesencephalic roots. Since both of the trochlear roots show 

 marked degeneration thi'oughout, it is highly probable that the 

 trochlear nucleus was affected by pressure from the growth of 

 this tumor. 



A glance at the mesencephalic root almost anywhere in its 

 course in the brain stem (fi'gs. 1 and 2, Mes.V.) shows a very 

 complete degeneration of its fibers. Inasmuch as the direct 

 injury of its fibers occurred in the region of the brachium 

 pontis, it would appear that the cells of origin were for the most 

 part located in the semilunar ganglion and that the mesen- 

 cephalic root fibers were mainly ascending. To test the truth of 

 this assumption I severed the left trigeminal roots of several 

 "guinea-pigs immediately behiind the semilunar ganglion and 

 traced the mesencephalic root centrally to the midbrain. From 

 these sections it is clear that the mesencephalic root contains 

 ascending fibers, but decidedly insufficient to account for the 

 marked degeneration of this tract in the series of the little girl. 

 From still later experiments, where the mesencephalic root in a 



1 Material was thoroughly fixed in 10 per cent formalin and washed in running 

 water. Pieces 5 to 10 mm. thick were placed for a week in a fluid of the following 

 proportions: Osmic acid, 1 gram; iodide of sodium (NaTs), 3 grams; water, 300 

 cc. It was finally washed in running water for twenty-four hours, dehydrated 

 thoroughly, and embedded in collodion. 



