THE MAMMALIAN NERVOUS SYSTEM 95 



longitudinal fibers of the pons (pyramidal, tract, etc.). The 

 two layers of pons fibers above mentioned belong to the super- 

 ficial system. Strip off the remaining superficial pons fibers 

 until the longitudinally directed pyramidal tracts are exposed. 

 The fibers of the brachium pontis will be now seen to inter- 

 digitate with the fascicles of longitudinal fibers. These fasci- 

 culi can be followed forward into the midbrain where they form 

 the most ventral fibers of the pedunculus cerebri. Expose 

 these longitudinally directed fibers for a short distance forward 

 (rostrad) and backward (caudad) of the pons. Do not com- 

 pletely dissect them, but leave them in place for future refer- 

 ence. They will be found to form three chief systems. The 

 most medial and the most lateral bundles of the fiber complex 

 which forms the ventral part of the cerebral peduncle in front 

 of the pons are cortico-pontile tracts from the cerebral cortex 

 to the pontile nuclei (cf. Herrick ('18), Figs. 75, 87), where, 

 after a synapse, their nervous impulses are taken up by the 

 neurons of the pontile nuclei and carried through the brachium 

 pontis to the cortex of the opposite cerebellar hemisphere. The 

 middle bundles of the cerebral peduncle contain the pyramidal 

 tract (tr. cortico-spinalis) which can be dissected through the 

 pons to reappear below on the ventral surface of the oblongata 

 as the pyramid (pyramis) . Its further course will be dissected 

 later. The chief constituent of the brachium pontis is thus 

 seen to be a system of fibers arising in the pontile nuclei for 

 carrying nervous impulses from the cerebral cortex (by the 

 cortico-pontile tracts) to the cerebellar hemispheres of the 

 opposite side. 



105. Brachium conjunctivwn. First examine the anterior 

 medullary velum (velum medullare anterius) , within which near 

 the median plane careful teasing will reveal a thin sheet of 

 fibers. 



The brachium conjunctivum (superior peduncle) forms 

 the medial part of the cerebellar peduncle complex at the point 

 where it joins the cerebellum (Fig. 11). Its fibers are directed 

 from the cerebellum forward and downward. Their further 

 dissection in the midbrain (decussation and connection with 

 the red nucleus) will not be taken up at this time. They 

 should, however, be dissected up into the cerebellum, where 



