OF THE GYRHS MARGINALTS AND GYRUS FORNTCATUS TN MONKEYS. 335 
complete (Nos. 10 and 11), and with scarcely any injnry to the marginal. In these, 
as well as in all the other cases recorded, there is well marked and extensive degene¬ 
ration in the crossed pyramidal tract. 
In the brains of Nos. 9 and 12 tliere were lesions otlier than that of the gyrus forni- 
catus. In No. 9 a considerable lesion in the hippocampal and under surface of the 
occipital regions had been effected, and in No. 12 lesions of both temporal lobes. 
But the degeneration which passes down into the spinal cord has in all the 
instances here investigated been coiifined to one tract—the lateral jjyramidal tract— 
mainly on the side opposite the lesion, and appears to have been in every case 
produced by the lesion of the gyrus marginadis or of the gyrus fornicatus.The 
region of the direct cerebellar tract is encroached upon in some instances (Nos. 2, 6, 7, 
and 8), but the extent, and twen the occurrence, of this encroachment has not appeared 
to me to bear any constant relation to the amount of lesion of the gjrus fornicatus, 
occurring, for example, in a case where there was little injury to the gyrus fornicatus, 
and not occurring in other cases after much more complete removal, although the 
animals lived three months or more. I conclude, therefore, that the apparent invasion 
of the direct cerebellar tract is due to some individual variation in the course of the 
fibres of the crossed pyramidal tract, and not to any degeneration of fibres belonging 
to the direct cerebellar tract itself I have not been able to make out with any 
certainty in my specimens the course of the degeneration in the internal capsule. 
In the mid-brain^ pons, and medidla (fig. 4b) the degeneration has the same appeai- 
ances as that following marginal lesions, and is found only in the pyramidal bundles 
on the same side as the lesion. 
In the spinal coixl the degeneration occupies the whole seetioncd area of the lateral 
pyramidal tract, and in the cervical region is no longer confined to the part bor¬ 
dering on the direct cerebellar tract, as was observed with degenerations following 
purely marginal lesions (compare fig. 5c with fig. 2d). 
In the upper dorsal region the extent and shape of the lesion is similar to that in 
the cervical region, but about the middle of the dorsal region it begins to diminish in 
extent, the outer and ^anterior part of the pyramidal tract assuming its normal 
appearance first. 
At the lumbar enlargement it is very much lessened in proportion, but is still 
distinct, being confined chiefly to the angle formed by the posterior root exit and 
circumference, as with the marginal degeneration. The degeneration can usually be 
traced as far as the fifth lumbar nerve, beyond which point I have not carried sections. 
Although following the course of the pyramidal tract by no means all the fibres of 
that tract are degenerated, many remaining normal. 
* I have ascertained that lesions of the hippocampal region alone are not followed by any perceptible 
degenerative changes in the spinal cord. 
