MESENCEPHALIC ROOT 201 



the mesencephalic root cells after a lesion of the N. ophthal- 

 micus and N. maxillaris; while Kosaka describes a few disin- 

 tegrated cells in the mesencephalic root nucleus following a 

 lesion of the N. maxillaris. Of these three investigators Kosaka 

 is the only one to claim any general cutaneous fibers arising 

 from the mesencephalic root nucleus and his results in the 

 monkey are diametrically opposed to those of May and Horsley. 



It is possible that there may be some variation in different 

 vertebrates concerning the distribution of the fibers from the 

 mesencephalic root nucleus and that some animals may have an 

 appreciable general sensory component, but the weight of evi- 

 dence thus far favors the conclusion that the descending fibers 

 of the mesencephalic root are concerned only with muscle sense. 

 This is certamly true for the guinea-pig, where after a lesion of 

 the mesencephalic root in the pons, the degenerated fibers were 

 traced in a series of Marchi sections solely to the masticator 

 muscle branches of the N. masticatorius. It might be mentioned 

 in this connection that degeneration shown by the Marchi 

 method is more convincing than a few disintegrated cells in 

 central nucleus as resulting from a peripheral lesion of its fibers. 

 For the chromatolysis method to be conclusive a number of cells 

 should be shown to have undergone degeneration. 



From the data at hand the writer would regard the mesen- 

 cephalic root as the muscle sense portion of the trigeminal nerve, 

 having its ganglion cells located both in the semilunar ganglion, 

 and in the midbrain and locus coeruleus. The peripheral proc- 

 esses of the latter constitute the so-called descending fibers, 

 which follow the trigeminal motor root fibers into the masseter, 

 pterygoid, and temporal branches of the nervus masticatorius. 

 The peripheral processes of these semilunar ganglion cells may 

 go through the mylohyoid branch of the nervus mandibularis to 

 the mylohyoid and digastric muscles; while their central proc- 

 esses enter the pons through the trigeminal sensory root and 

 constitute the so-called ascending fibers of the mesencephalic 

 root. Fibers and collaterals from this system are distributed 

 to the trigeminal motor nucleus and to a group of small cells 

 situated medial and dorsal to the trigeminal sensory nucleus. 



