1932] Poliak: Afferent Fiber Systems, Primate Cerehral Cortex 71 



terminate in the basal nuclei and in the cerebral cortex as alleged, 

 must be studied by other experiments. There are indications that the 

 medial nucleus of the thalamus receives a part of the intermediate 

 somato-sensory tracts by way of the internal medullary lamina. But 

 no evidence was found that any such fibers terminate in the so-called 

 dorsal or anterior nucleus. 



2. DESCENDING CJORTICO-THALAMIC AND OTHER COBTICO-FUGAL 

 FIBERS 



The existence of an extensive descending cortico-thalamic fiber 

 system, which according to some investigators plays an important role 

 in normal and in pathological somato-sensorj^ function (Head, Wallen- 

 berg, see also Long, Melius, Ramon y Cajal, Probst, Hollander, Villa- 

 verde, and my paper, 1926), cannot definitely be denied, although 

 fibers of this character are somewhat more numerous only in the most 

 ventral zone of the ventro-lateral nucleus. (See also Minkowski, 1923- 

 24, and Riese, 1925.) 



The bulk of the fibers which degenerate after the destruction of 

 the occipito-parietal cortex and enter the caudal portion of the 

 thalamus, especially the pulvinar, certainly reach the midbrain by way 

 of the brachium of the superior colliculus. (In Experiment XV, figs. 

 95, 96, not further reported here, the area peri-parastriata of Elliot 

 Smith, areas 18 and 19 of Brodmann, or field 19-a of Vogt was 

 destroyed ; whether some of these fibers may, nevertheless, terminate in 

 the thalamus or give off collaterals during their passage through the 

 thalamus cannot be decided by Marehi 's method and must be studied 

 by Golgi's method in higher mammals and in man; scarcely any of 

 these fibers originate in the area striata itself, see figs. 86-94 of 

 Experiment XIV. ) This fact, together with the findings of Brouwer 

 and Zeeman, and of Overbosch, — that no peripheral afferent optic 

 fibers enter the thalamus (pulvinar), — militates against the view 

 which regards both the thalamus and midbrain as subcortical stations 

 for the cortico-petal visual impulses. (Compare Visual System). 



Other numerous cortico-fugal fibers descending from the precentral 

 and frontal cortical regions (both regions are taken as a unit; a 

 detailed analysis of these different tracts according to areas will be 

 given at a later time) , are : 



(1) very numerous and quite fine fibers to the caudate nucleus 

 (tractus cortico-caudatus) by way of the subcallosal stratum and the 



