200 



WILLIAM F. ALLEN 



It was stated that many fibers and collaterals from both the 

 ascending and descending mesencephalic root fibers went to the 

 trigeminal motor nucleus and to a group of small cells situated 

 medial and dorsal to the trigeminal sensory nucleus. The former 

 evidently form reflex arcs with the motor cells and the latter 

 may be a muscle sense relay station (?) to the cerebral cortex, 

 like the sensory nucleus (substantia gelatinosa) for the cutaneous 

 sense fibers. 



• Little was accomplished in the way of observations on animals 

 for the reason that there were many obstacles encountered in 

 making satisfactory lesions that would destroy all muscle sense 

 fibers going to the masticator muscles. To be absolutely certain 

 of accomplishing this, it would be necessary to destroy both 

 semilunar ganglions and the motor roots passing through them 

 or the equivalent, which would of course result in a complete 

 paralysis of the masticator muscles. In those experiments where 

 the left mesencephalic root was severed in the pons, with little 

 damage to the brachium conjunctivum, no difference could be 

 detected in the action of the left masticator muscles in these 

 animals and those of normal animals. Something interesting 

 might result in severing both inesencephalic roots in the pons of 

 an animal and testing its ability to compete with a normal 

 animal in eating blindfolded a mixture of lettuce and tough 

 roots. Also muscle spindle preparations from the masseter 

 muscles of an animal having its mesencephalic roots severed in 

 the pons would likely show some degeneration. 



The results of the previous experimental work on the mesen- 

 cephahc root, which have been obtained mainly from counting 

 the chromatolytic cells in the mesencephalic root nucleus after 

 severing certain branches of the trigeminal nerve, may be sum- 

 marized as follows: For the rabbit Willems and Kosaka found 

 no chromatolytic cells in the mesencephalic root nucleus, except 

 after severing the N. mandibularis or its motor branches. In 

 the dog Kosaka found a few degenerated cells in the mesen- 

 cephalic root nucleus after destroying the N. maxillaris and 

 certain sensory branches of the N. mandibularis. In the monkey 

 May and Horsley found absolutely no chromatolysis in any of 



