42 Vniversity of California Publications in Anatomy V'^oi.. 2 



Experiment V-a 



In this experiment, as in those preceding:, an attempt was made to 

 interrupt partly or totally the thalamo-eortieal radiation near its 

 origin and to study it by means of Marchi's method. With this intent 

 a small hook-shaped lancet used in ophthalmology was thrust in a 

 young Java monkey, through the lower part of the left angular con- 

 volution (or, what means the same, through the most posterior part 

 of the second temporal convolution), immediately in front of the 

 collateral sulcus. (Small coarsely stippled area in fig. 4.) 



Fourteen days later the animal was killed. The lesion, as the 

 macroscopic and microscopic examination of the left hemisphere shows, 

 consists of a small superficial damage (1-2 millimeters in diameter) 

 exactly between the collateral and the superior temporal sulcus. The 

 rest of the brain appears absolutely normal. From the superficial 

 lesion a channel begins which is directed orally and somewhat 

 medially as it penetrates the superior temporal convolution and 

 the dorsal half of the putamen until it reaches the internal capsule 

 between the putamen laterally and the thalamus and the caudate 

 nucleus medially. (Compare L in fig. 5.) (On the lesion in the same 

 case causing a partial interruption of the visual radiation see Visual 

 System, Chapter XIV, Experiment V-A.) In this way the auditory 

 radiation passing through the ventro-caudal portion of the putamen 

 almost completely escaped injury. (4 in fig. 5 corresponds with figs. 

 29 and 49.) The damaged portion of the internal capsule corresponds 

 with its middle third, forming the ''knee" of the capsule, while its 

 anterior and posterior portions remain undamaged. Especially the 

 most anterior portion of the capsule, bordering on the anterior pole 

 of the thalamus, remains outside the injury {1 in fig. 5). The lesion 

 of the internal capsule represents a single well delimited focus; the 

 ascending fibers of the capsule interrupted by the lesion also represent 

 one single sheet or "fan" of the thalamo-cortical radiation. In addi- 

 tion to this there is a narrow horizontal injury to the pulvinar of the 

 thalamus, which is connected with the second injury causing the 

 damag^e to the visual radiation. 



The degenerated fibers of the thalamo-cortical radiation ascend 

 from the internal capsule at the beginning as compact bundles, becom- 

 ing somewhat loose within the centrum semiovale, and farther toward 

 the central furrow, forming, on the whole, a well defined fiber system. 



