THE TEGMENTUM OF THE CRUS CEREBRI AND ITS GANGLIA. 447 



wit, the roots of the fifth nerve. These last arise in the most 

 external band of the grey matter around the aquseductus Sylvii, 

 from small clusters of large vesicular cells having a long diameter 

 of 60 n and a breadth of from 45 to 50 p (fig. 249, 7), and form 

 after a time a chain of transverse sections of fasciculi, which > 

 arranged in the form of a flat arch, are applied to the external 

 surface of the thick-walled tube of the aqueduct (figs. 250 

 and 251, 5'). 



We see, therefore, that even at this height a relation exists 

 in the disposition of the motor and sensory masses of origin, 

 which is persistent through the whole grey matter of the 



Fig. 251. 



Fig. 251. Transparent transverse section of the pons of Man, at the 

 plane of emergence of the fourth pair of nerves. A, Central grey 

 matter of the ventricles surrounding the aqeduct ; 4, decussation of 

 the fourth nerve in the superior cerebral valve (valve of Vieussens) ; 

 4', transverse section of a fasciculus belonging to the fourth nerve ; 

 5, substantia ferruginea ; 5', chain of the descending roots of the fifth 

 nerve ; L, posterior longitudinal fasciculus ; BA, transverse section of 

 the superior peduncle (processus a cerebello ad cerebrum) as they pass 

 from the decussation ; VS, fascicuil of the spinal cord situated inter- 

 nally to the superior cerebellar peduncle ; m, loop layer from the 

 nates ; s, loop layer from the testes. 



central cavities; the former as a rule occupying a position 

 near the median line, and in front ; the latter being situated 

 more laterally, and at the same time posteriorly ; their nerves 

 consequently being analogous to the anterior and posterior 

 roots of the spinal nerves. 



In the pons and in the medulla oblongata, as Deiters has 

 correctly pointed out, there is a median lateral tract belonging 

 to the roots of cerebral nerves, situated between the median 

 and the lateral (posterior) tracts. 



