488 THE BRAIN OF MAMMALS, BY TH. MEYNEBT. 



of the pons in the form of large richly pigmented bodies 

 arranged radially to the grey floor, with radial nerve fibres 

 running to meet it ; perhaps in their course (which will pre- 

 sently be described) they also contribute roots to the fifth. 

 Black pigmented cells are found similarly scattered in the roof 

 of the fourth ventricle internally to the superior peduncle 

 (substantia ferruginea superior). In the brains of children, and 

 in those of Mammals, these cells lose their pigment, like those of 

 Soemmering's substance, and indeed in many corpuscles of this 

 formation pigment does not appear to be developed. 



The fasciculi of the fifth, proceeding from the substantia 

 ferruginea, form a stratum having a thickness of 0'8 of a milli- 

 meter which runs transversely inward beneath the grey floor of 

 the fourth ventricle ; they then penetrate, interlace with, and 

 encircle, the posterior longitudinal fasciculi, and finally cross 

 the median line by means of an acute-angled decussation passing 

 partly between and partly in front of the posterior longitudinal 

 fasciculi, the decussating fibres being at the same time arched, 

 with their convexity directed upwards. Having arrived at the 

 opposite side, they pass outward, partly through and partly in 

 front of the other posterior longitudinal fasciculi, and turn 

 forward to enter the tract of the great root of the fifth as the 

 middle set of the chain of fasciculi surrounding the grey floor 

 (figs. 252, 253, 5 6). 



Both the interlacement of the posterior longitudinal fasciculus 

 seen on transverse section, and, in particular, the region sur- 

 rounding it anteriorly, as far as to the margin of the posterior 

 division of the pons, is very rich in nerve corpuscles of a large 

 size, that are sparingly present, and of a far smaller variety that 

 are more closely clustered. The middle descending root of the 

 fifth appears to me to be continuous with the larger form of 

 corpuscles. 



The internal division of the descending roots of the fifth is 

 derived, in all probability, from the longitudinal fasciculi of the 

 anterior division of the pons (crusta of the cerebral peduncle), 

 and runs in the form of straight fasciculi of the raphe from the 

 anterior division of the pons into the posterior. After under- 

 going decussation at acute angles, the fasciculi curve partly in 

 front of the posterior longitudinal fasciculi, partly run trans- 



