456 



THE BRAIN 



Basis Pedunculi (O.T. cnista). The basis pedunculi is 

 somewhat crescentic when seen in section, and stands quite 

 apart from its fellow of the opposite side. It is composed of 

 a compact mass of longitudinally directed nerve fibres which 

 are carried upwards into the internal capsule. The inter- 

 mediate three-fifths of each basis pedunculi is formed, almost 

 entirely, by the important cerebro-spinal fasciculus (O.T. pyra- 



Inferior quadrigeminal body 



Grey matter of _ 

 aqueduct 



Aquaeductusj__ 

 cerehri \ " 



^Mesencephalic root of trigeminal nerve 



^'Nucleus of trochlear nerve 

 - Inferior brachium 

 v ,,-- Medial longitudinal fasciculus 



Raph 



Brachium conjunct! vum 



Substantia nigra 



Basis pedunculi 



FIG. 1 80. Transverse section through the Mesencephalon at the level of the 

 inferior quadrigeminal body : the right side only is reproduced. The 

 drawing is taken from a Weigert-Pal specimen, and therefore the grey 

 matter is pale and the strands of white matter are dark. The dark colour 

 of the substantia nigra is not evident owing to the thinness of the section. 



midal tract) as it descends from the motor area of the cerebral 

 cortex, but the cerebro-spinal fasciculus is quite indistinguish- 

 able, under ordinary circumstances, from the fronto-pontine 

 fibres on its medial side and the temporo-pontine fibres on its 

 lateral side. 



Tegmentum. Unlike the bases pedunculi, the tegmentum 

 is undivided, a faint line in the median plane, termed the 

 median raphe, alone indicating that it consists of a right and 



