240 ANATOMY OF THE CENTEAL NEEVOUS SYSTEM. 



rabbit). It probably consists (Beevor) of several separate parts, and does 

 not entirely degenerate after section (see Pigs. 169 to 172). 



The fasciculus longitudinalis inferior, a very large tract of fibers, con- 

 nects the temporal lobe with the occipital lobe (see Figs. 186 to 188). 



Dijirlne, who has' studied this bundle very thoroughly in its relations to many 

 other parts of the fiber-systems of the brain, observed that it was degenerated in a 

 case of pure Word-blindness. This fact and the course of the tract make it very 

 probable that essentially it serves to carry optical impressions to other parts of the 

 brain. It exists in other Primates also. Flechsig has lately felt compelled, as a 

 result of embryological studies, to exclude this bundle entirely from the system of 

 association-pathways. It is said not to terminate in the temporal lobe, but to curve 

 up near the apex of the same, into the thalamus; so that it would consequently be a 

 part of the radiatio occipito-thalamlca. 



Sachs justly emphasizes the fact that the temporal lobe is really con- 

 nected with all the remaining parts of the brain by means of long tracts 

 only. There is localized in it, as the researches of pathology show, the 

 auditory imagery of speech. The very abundant possibilities of communi- 

 cation may correspond to the importance which such auditory factors have 

 in human thought. 



In Pig. 156 the long association-pathways above mentioned are com- 

 bined diagrammatically. One tract only is not included there, because until 

 recently it was very questionable whether or not it represented a long asso- 

 ciation-pathway. It is the fasciculus fronto-occipitalis. Arising from the 

 medullary covering of the posterior and lateral horns of the ventricle, its 

 fibers pass forward as a well-defined bundle external to the lateral ventricle. 

 They always keep close beneath the corpus callosum and on the dorsal edge 

 of the nucleus caudatus (see Pigs. 170 to 172). 



It is the same tract that I designated earlier as the association-bundle of the 

 caudate nucleus (Fig. 168). Investigations by Diib'ine, Rietx, and Muratow have 

 shown, however, that we are here really concerned, as Forel and Onufrowicz had 

 conjectured, Avith an association-bundle between the medulla of the occipital lobe 

 and that of the frontal pole. Consequently, the bundle will be found designated as 

 the fasciculus fronto-occipitalis in the large frontal sections through the entire brain, 

 to be shown later. Moreover, the smaller part only of this tract of fibers is, like all 

 longer association- bundles, composed of fibers of very great length; a, far greater 

 part consists of fibers that connect together single sections of its long course. 



It is perfectly proper to designate all of these long tracts as interlobular 

 association-bundles, and to distinguish them from those that connect with 

 one another separate points within this or that lobe. These intralobular 

 tracts have been little studied hitherto. They are best known for the occipi- 

 tal lobe, where pathways have been demonstrated by Saclis, Wernicl-e, Viault, 

 and others, which are adapted to connect with one another various regions 

 and layers of this lobe in all directions. 



