( 41 ) 



accompanying fibres; according (o Hulles '), this is also the case in 

 the pig. A well isolated exit is seldom to be seen owing to the fibres 

 not running compactly to the periphery and to their being apparently 

 interrupted by the masticatory nucleus. Where the tracing of the 

 mesenc. fibres is possible {tamandua tetradactyld), its exit in the 

 ventral part of the rad. spinalis trigeminis is clear; in this animal 

 a wide separation from the more ventrally running motor quintus 

 root is easily distinguishable. 



What can be seen in all the other mammals is that fibres from 

 the region of the rad. mesenc. turn venlro-laterally and reach the 

 periphery close to the motor nerve. The latter passes through the 

 pia, ventrally from the sens, or radix. si)inal.; the mesenc. fibres in 

 any case do not come to lie ventrally from the motor root. 



Summing up the results of this investigation, the conclusions are 

 as follows : 



1. In all animals, -where the exit of the mesenc. quintus root 

 can be traced ^vith certainty, this takes place dorsally to the motor 

 root. 



2. In all these animals (scyllium canicula v. i.) it leaves the 

 oblongata hetn-een the jihres of the sens, trigeminus root, in teleostei 

 perhaps even slightly dorsally to them. Whether it runs extra-bulbar 

 for a part with the sens, root and its collaterals, is uncertain, but 

 it is not rendered improbable by the above-mentioned pathological 

 observation. 



3. In scyllium canicula the mesenc. quintus root leaves in two 

 w^ays the oblongata: one part orally to the sens, root, and one part 

 in the way as mentioned sub. 2. The first part is, however, accom- 

 panied by a more ventral motor V stem. 



4. The primitive position of the mesenc. quintus nucleus is do r.sal 

 in the tectum opticum, not distally from it. The variations herein 

 in lower animals ave partly due to differences in the structure in 

 the mid-brain. In the lowest order of mammals vinonotremata and 

 marsupials) this position is seen again in principle. Moreover in 

 marsupialia especially (didelphys) the nucleus consists of different 

 kinds of cells, just as in some reptiles ; while in fishes one 

 form of cell (clumsy-polyedric), and in higher mammals and birds the 

 other (round, oval, vesicular) predominates or is exclusively present. 



5. The distal spreading of the nucleus, most marked in insectivora. 



^) HuLLEs: Vergl. Anatomie der cerebr. Trigeminusvviirzel. Obersteiners Arbeiten. 

 1908- 



/ 



