INTERNAL STRUCTURE OF THE PONS 



conjunctivum, which increases in volume as it is followed rostrally, reaching its 

 maximum in the mesencephalon at the level of the inferior colliculi. In this 

 decussation the fibers of the brachium undergo a complete crossing. 



The ventral spinocerebellar tract, which has made its way through the retic- 

 ular formation of the pons, turns dorsolaterally near the rostral end of the 

 pons, winds around the brachium conjunctivum, and enters the anterior medul- 

 lary velum, in which it descends to the vermis of the cerebellum (Figs. 110, 

 149). 



Fourth ventricle 

 Dorsal longitudinal fasciculus 

 Medial longitudinal fasciculus 



Thalamo-olwary 

 Brachium conjunctivum 



tract 



Decussation of brachium 

 conjunctivum 



Trochlear nerve 



Mesencephalic root of trigeminal 

 nerve 



Lateral lemniscus and nucleus 

 Dorsal nucleus oflegmentum 

 Ventral nucleus of 



tegmentum 



Nucleus centralis superior 

 Medial lemniscus 

 Pons 



Fig. 112. Dorsal half of a section through the rostral part of the human pons. The index 

 line to the mesencephalic root of the trigeminal nerve does not quite reach that structure. Pal- 

 Weigert method. 



The lateral lemniscus is an important tract of fibers which we have already 

 traced from the cochlear nuclei by way of the trapezoid body and striae medul- 

 lares acusticae. It first takes definite shape about the middle of the pons, where 

 it is situated lateral to the medial lemniscus (Fig. 110). As it ascends it becomes 

 displaced dorsolaterally until it occupies a position on the lateral aspect of the 

 brachium conjunctivum (Fig. 112). In this position there is developed in con- 

 nection with it a collection of nerve-cells, the nucleus of the lateral lemniscus, 

 to which its fibers give off collaterals. 



