30 University of California Puhlications in Anatomy [Vol. 2 



trate the ventral portion of the internal capsule and form there arch- 

 like bundles between the putamen and thalamus. The most lateral of 

 them even pass through the substance of the putamen. On the whole, 

 they form the lateral bundles of the thalamo-cortical radiation which, 

 closely pressed to the claustrum, ascend toward the ventrolateral 

 (opercular) segments of both central convolutions (figs. 30-34). 

 Accordingly, fiber groups from the uppermost portion of the dorso- 

 lateral nucleus are the most dorso-medial part of the radiation ; those 

 from the ventro-lateral nucleus are the most ventro-lateral ; the 

 remaining bundles are the intermediate portion. All these fiber 

 bundles together form, in fact, individual "fans" arranged dorso- 

 ventrally. The fans in turn are arrayed perpendicularly and some- 

 what obliquely with respect to the long axis of the hemisphere, or, 

 in other words, to the long axis of the thalamus. They follow con- 

 secutively one behind the other : the most oral fan emerging from the 

 most oral portion of the thalamus, the most caudal (posterior) fan 

 from the most caudal portion, the middle fan from the middle portion. 

 (Compare Experiment V-a.) 



Moreover, it is evident that the thalamo-cortical radiation together 

 with the acoustic radiation {ar in corresponding figures) arising from 

 the internal geniculate body forms a huge system of diencephalo- 

 cortical fibers wherein the acoustic radiation occupies a most ventral 

 position. The visual radiation (vr in corresponding figures), as will 

 be shown later (see Visual System), forms a part of the diencephalo- 

 cortical fiber system only at its beginning within the internal capsule, 

 diverging from the common somato-sensory-acoustic portion of the 

 mentioned system as it approaches the occipital cortex. 



Thus, considering only the individual bundles or "radii" of the 

 thalamo-cortical radiation forming the described "fans" there is an 

 uninterrupted chain of such "radii" arranged or segmented both 

 longitudinally and perpendicularly with respect to the long axis of 

 the hemisphere. These radii are, on the whole, at their thalamic origin 

 near one another, and diverge as they approach the cortex. 



In certain sections (figs. 30-34) it is even difficult because of 

 their proximity to distinguish ventral bundles originating in the 

 ventro-lateral thalamic nucleus (and perhaps also in the hypo- 

 thalamus) from the central acoustic path. Only by tracing the further 

 course of the acoustic bundles toward the superior temporal convolu- 

 tion (Ti in corresponding figures) along the lower lip of the Sylvian 

 fossa (FS) and the course of the ventral thalamo-cortical bundles 



