60 Anatomy of the Nervous System 



fibres run into the corresponding nucleus of the other side 

 and curve dorsally in the lemniscus to end in the posterior 

 colliculus (Papez). 



Ventrally, the medial lemniscus continues forward in the 

 same position which it occupied in the hindbrain, becoming 

 more flattened dorso-ventrally, however, and soon moving 

 aw^ay from the raphe to a somewhat more lateral position, 

 where it may be traced up into the thalamus. 



In the dorsal part of the tegmentum, on the other hand, 

 the medial longitudinal bundle likewise continues forward 

 in the same position where it was observed farther back. It 

 also becomes more flattened dorso-ventrally, and it breaks 

 up into a number of distinct, compact, little bundles. At the 

 level of the trochlear nucleus, it forms a dorsal concavity 

 containing the nucleus, and some of its fascicles run right 

 through the latter (PI. XIII.). Then it swings round dorso- 

 medially so that at the level of the more anterior part of the 

 oculomotor nucleus the tracts of the two sides enclose be- 

 tween them a \^-shaped area of the central gray, in which 

 the nerve nuclei lie. In front of these nuclei, the ventral edges 

 of the two tracts separate a little before they continue into 

 the hypothalamus. Here the tract disappears in relation 

 with a small group of cells, the interstitial micleiis of Cajal, 

 situated at the anterior extremity of the red nucleus (vide 

 infra) and just lateral to the tract itself (PI. X\\). This 

 nucleus gives rise to the interstitio-spinal tract {Tract of Boyce), 

 which in the rat is a bundle of coarse fibres running back in 

 first the dorsal and then the medial part of the medial longi- 

 tudinal fasciculus. It gives off fibres to the eye-muscle 

 nuclei and passes on into the spinal cord, taking up a sulco- 

 marginal position there (Papez). In the lateral part of the 

 medial longitudinal bundle, for a considerable distance 

 through the midbrain, run secondary fibres from the nucleus 

 of Deiters to the oculomotor and trochlear nuclei (ascending 

 tract of Deiters). 



