132 



ANATOMY OF THE CENTEAL NERVOUS SYSTEM. 



feature. The first is the Fasciculus longitudinalis posterior (Fig. 44). It 

 arises with its most anterior fibers from a single nucleus of the most posterior 

 part of the Thalamus, but reinforces itself in its backward course, while it 

 passes the nucleus of the Oeulomotorius. The bundle lies on either side of 

 the middle line quite dorsally, partly imbedded in the nuclei in question and 

 partly yentral to them (Fig. 65). In a similar way from a nucleus which is 

 readily to be seen in the ventral part of the thalamencephalon in all lower 

 vertebrates — Nucleus tegmenti — arises the Tractus tegmento-cerebellaris, — 

 the peduncle of the cerebellum. It traverses the midbrain for only a short 



■J^ 



Fig. 72. — Sagittal section of brain of chick on eighth day after hatching, 

 showing origin of the Faac. long, lateralis. 



distance, and crosses to the other side just behind the last roots of the Oeulo- 

 motorius (see Fig. 65). The decussation of the Tractus tegmento-cere- 

 bellaris lies dorsal to the decussation of the tegmental tract from the roof: 

 Commissura ansulata. 



The third longitudinal fasciculus of the midbrain-basis arises from the 

 commissura posterior (Figs. 69 and 73), whose limbs turn backward after 

 the decussation quite anterior to the midbrain-roof, describing the out- 

 line of a horseshoe. The posterior end is still unknown. There is strong 

 evidence that in the lateral parts of the posterior longitudinal bundle fibers 

 from that commissure pass far back. According to KoUiker and others, 



