COETEX OF FOREBEAIN AND MBDITLLA OF HEMISPHERES. 



239 



of the cortex to another or over the entire brain occur precisely by way of the flbrae 

 proprisB. Many other ways are presented, as, for instance, the fine net-worlc of 

 nerve-iibera on the surface of the cortex; then, too, the entire cortex may be in- 

 fluenced simultaneously by a variation in the volume of blood in its vessels. 



The tracing of the fibrse proprise between two neighboring cortical 

 regions is not extremely difficult if the teasing method is employed. The 

 demonstration of connections between regions lying farther apart from one 

 another is much more difficult and leads very easily to artefacts, which cor- 

 respond in part to the actual direction of the fibers. A few tracts only are 

 to be followed with some degree of certainty. Such are the fasciculus un- 

 cinatus, the fasciculus arcuatus, the fasciculus longitudinalis inferior, the 

 cingulum, and a few others. 



Fig. 156. — Diagram of the course of the long association-pathways. 



The fasciculus uncinatus arises from the cortex of the temporal lobe, 

 passes forward close to the ventral margin of the insula, and becomes lost in 

 the most ventral regions of the frontal lobe (Figs. 170 to 173). The fas- 

 ciculus arcuatus passes along over the dorsal part of the insula from the 

 more posterior portion of the temporal lobe to the cortex of the parietal 

 and frontal lobes. Fibers accompany it (doubtful) which arise in the frontal 

 lobe and terminate in the cortex of the occipital lobe (see Figs. 169 to 172). 



The cingulum is a long tract that runs in the marginal gyrus — the gyrus 

 fornicatus — from the cortex of the cornu Ammonis to the most ventral 

 region of the frontal lobe, and perhaps to the olfactory lobe also (dog and 



