236 Relations of the Frontal Lobe in the Monkey 
missure, in the mesial tract in the crus and in the corresponding portions 
of the pons, which disappeared before reaching the lower levels. 
Von Monakow’s case* of an extensive destruction of cortex of contig- 
uous portions of the second and third frontal convolutions shows almost 
complete destruction of the mesial segment of the crus, but it is not 
clear that there is much degeneration in the anterior segment of the 
internal capsule. In this case there is also extensive destruction of sub- 
cortical tissue, which complicates the question of the origin of the fibers 
degenerated in the crus. 
Dejerine* believes that the fibers of this tract arise in the cortex of 
the frontal and Rolandic operculum, but suggests that some of its fibers 
may come from the orbital surface of the third frontal convolution. He 
bases his conclusions upon the study of degenerations following such 
extensive lesions that the possibility of error does not seem to be excluded. 
These experiments seem to show that the mesial segment of the crus 
does not contain any cortico-pontine fibers coming by way of the anterior 
segment of the internal capsule. In an extensive series of experimental 
ablations of small areas of cortex in the Rolandic and frontal operculum 
in the monkey (Fig. 20), I have never observed any degeneration in the 
mesial segment of the crus. Degenerations from such lesions always 
enter the internal capsule in levels above the highest levels of the anterior 
segment. In all my experimental ablations of the so-called facial area of 
the cortex the degenerated fibers have been found in the posterior segment 
of the internal capsule.” The genu of the internal capsule, like the mesial 
segment of the crus, was entirely free from degeneration. It can hardly 
be claimed, as yet, that it has been shown that the fibers of the mesial 
seoment of the crus constitute a definite tract arising in limited areas of 
the cortex of the frontal lobe. If, as is claimed by Dejerine, the crus 
is made up of cortical projection fibers only, the cells of origin of the 
mesial segment will be found in the cortex either of the frontal lobe or of 
the island of Reil. I think Dejerine wrong in the statement that the 
fibers of the genu (“véritable faisceau géniculé”) come from the 
anterior segment (Vol. 2, p. 30), In his “ Cas Morceau ” (Vol. 2, p. 148), 
the anterior segment of the capsule is apparently completely destroyed, 
’Nothnagel: Gehirnpathologie, Vol. IX, Wien, 1897. 
* Anatomie des Centres Nerveux, Tome II, Paris, 1901. 
5 Hxperimental Degeneration Following Unilateral Lesions of the Cortex 
Cerebri, Proc. Royal Society of London, Vol. LVIII. Motor Paths in the Brain 
and Cord of the Monkey, Journal of Nervous and Mental Diseases, April, 
1899. 
