272 C. JUDSON HERRICK 



of this nucleus and extending somewhat dorsally of the ventric- 

 ular eminence formed by it (figs. 8, 23, 59, 60, nucxom.posL). 

 These neurons form the nucleus of the posterior commissure, as 

 already described (p. 252), and are grouped among the terminals 

 of this commissure. They might with equal propriety be called 

 the nucleus of the fasciculus longitudinahs medialis, for they 

 appear to be differentiated to receive nervous impulses from 

 the tectum by way of the commissura posterior and to transmit 

 these impulses into the fasciculus lor.c'itudinalis medialis. In 

 higher vertebrates separate nuclei for these two tracts are de- 

 scribed in this region, but in Necturus this differentiation seems 

 not to have taken place. 



Some fibers of the fasciculus longitudinalis medialis decussate 

 in the commissure of the tuberculum posterius. The fasciculus 

 rapidly increases in size as it is followed caudad and below the 

 level of the fovea isthmi (figs. 11 to 14 ) it is composed of several 

 fascicles of heavily myelinated fibers. There is a particularly 

 strong decussation of the fibers of the fasciculus both rostrad 

 and caudad of the fovea isthmi, (figs. 46, 47). As the medulla 

 oblongata is approached, this fasciculus, like the other members 

 of the motor tegmentum, diminishes in size, largely by dis- 

 charge of its fibers among the neurons of the eminentia sub- 

 cerebellaris tegmenti. The larger number of its fibers, however, 

 accompany the remnant of the fibers of the ventral tegmental 

 fascicles into the medulla oblongata. 



26. Tractus tegmento-interpeduncularis 



This name is given provisionally to a well defined fascicle of 

 fibers of uncertain significance. They are unmyehnated and extend 

 forward and ventralward from the eminentia subcerebellaris 

 tegmenti at the boundary between the gray and white layers, 

 running parallel with the brachium conjunctivum and a little 

 rostrally of it. The tracts of the two sides converge at the 

 fovea isthmi, immediately caudad of which they turn abruptly 

 ventralward close to the median plane and spread out in the 

 dense neuropil of the interpeduncular nucleus, which occupies 



