THE INTERNAL STRUCTURE OF THE MESENCEPHALON 



159 



minate fibers from the interpeduncular ganglion (Fig. 211). The tegmentum 

 contains many longitudinal fiber tracts which are continued into it from the dor- 

 sal part of the pons. The most conspicuous of these is the brachium conjunc- 

 tivum. 



The Decussation of the Brachia Conjunctiva. In the sections of the pons we 

 saw that, as the brachia conjunctiva ascend toward the mesencephalon, they 

 sink deeper and deeper into the pars dorsalis pontis (Fig. 112). When they 

 reach the level of the inferior colliculi of the corpora quadrigemina they are 



Aqueduct of cerebrum 



Mesencephalic root of N. V 



Medial longitudinal 

 fasciculus 



Decussation of brachium 

 conjunctivum 



Interpeduncular fossa 

 Szibstantia nigra 



Commissure of inferior colliculi 

 Inferior quadrigeminal brachium 

 Nucleus of inferior colliculus 

 Lateral lemniscus 

 Trochlear nerve 

 Thalamo-olivary tract 

 Nucleus of trochlear nerve 



Medial lemniscus 

 Basis pedunculi 

 Posterior perforated substance 

 Pons 



Fig. 114. Section through the mesencephalon of a child at the level of the inferior colliculus. 



Pal-Weigert method. (X 4.) 



deeply placed in the tegmentum; and here they cross the median plane in the 

 decussation of the brachium conjunctivum (Fig. 114). After crossing, each brach- 

 ium turns rostrally and forms a rounded bundle of ascending fibers, which al- 

 most at once comes into relation with the red nucleus (Fig. 116). Many of the 

 fibers enter this nucleus directly, while others are prolonged over its surface to 

 form a capsule that is best developed on its medial surface. While the majority 

 of these fibers ultimately end in the red nucleus, some reach and end within the 

 ventral part of the thalamus (Fig. 115). By way of summary we may repeat 

 that the fibers of the brachium conjunctivum, or at least the greater part of them, 



