LECTURE VIII. 



THE PONS AND THE CEREBELLUM. 



GENTLEMEN : We learned in the last lecture that the 

 bundles of fibres from the fore- and inter- brains arranged them- 

 selves into two layers in the region of the mid-brain. These 

 layers were called the crusta or pes pedunculi and the tegmen- 

 tum. Back of the corpora quadrigemina the aqueduct becomes 

 markedly broader. Both pes and tegmentum pass under it and 

 farther back into the hind-brain. Only one division of the teg- 

 mentum, the anterior peduncles of the cerebellum, arising in 

 the red nucleus, now passes dorsad from the floor of the mid- 

 brain to the roof of the hind-brain. From this roof has been 

 developed the cerebellum in adults. The space lying under it, 

 the continuation of the aqueduct, is called the ventriculus 

 quartus. The prolongations of the crusta and tegmentum are 

 contained in the floor and lateral portions of the hind-brain. 



Let us first see what becomes of the fibres of the pes. Not 

 far back of the corpora quadrigemina a thick mass of white 

 fibres is laid across the crusta. Arising from the cerebellum, 

 they pass down, surround, and cover the region of the pes in a 

 thick layer. Taken together, these fibres are called the pons. 



Only a portion of these fibres cover in the surface of the 

 crusta (stratum superficial pontis) ; the majority of them dip in 

 between the fibres of the latter, and divide them into isolated 

 bands (stratum complexum et profundum pontis). 



You will remember that of the fibres which r>ass downward 

 from the brain in the crusta a part could only be traced as far 

 as the pons. They were the fasciculi from the frontal, parietal, 

 and temporal lobes. The pyramidal tract from the central con- 

 volutions passes through and below the pons. Almost the 



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