956 



THE NER VE SYSTEM 



(a) The uncinate fasciculus (/. unciuatus) passes between the uncinate gyre and 

 the orbital portion of the frontal lobe; in its course it curves beneath the depths 

 of the basisylvian fissure (Fig. 709). 



(6) The superior longitudinal fasciculus (f. longitudinalis superior) (Fig. 709) 

 is beneath the convex surface of the hemisphere arching over the lenticular 

 nucleus. It joins the frontal cortex with the parietal and temporal cortex and 

 brings into relation the motor speech centres and the centres of auditory and 

 visual memories. 



(c) The inferior longitudinal fasciculus (f. longitudinalis inferior) is usually 

 described as a tract associating the centres of auditory and visual memory. Such 

 association fibres undoubtedly exist, but it is doubtful whether they are collected 

 into a distinct fasciculus. The bundle which is usually designated by this term 



FIG. 709. Diagram showing the principal systems of associating fibres in the cerebrum. 



has been proved to be in part the projection system between the occipital cortex 

 and the thalamus and external geniculate body (E. Redlich) and in part also the 

 fibres from the temporal cortex (meditemporal and subtemporal gyre) to the 

 crusta. 



(d) The cingulum, also called the fornix periphericus, is a band of white fibres 

 that course in the white substance of the callosal gyre and runs excentrically 

 to the corpus callosum. Its fibres may be traced frontad into the mesal olfactory 

 stria and the anterior perforated substance, while caudad they radiate into the 

 hippocampus. It may be regarded as an association tract of the rhinencephalon 

 akin to the fornix. 



(e) The fasciculus rectus or perpendicular fasciculus runs dorsoventrad in the 

 occipitoparietal transition and associates the subparietal gyres with the medi- 

 and subtemporal gyres; a part of the fasciculus associates the dorsal occipital 

 region with its ventral part and with the subcollateral gyre (Fig. 709). 



The fornix, previously described, may be enumerated among the long associa- 

 tion tracts; it belongs exclusively to the olfactory apparatus. 



2. The commissural fibres are grouped under the following heads: (a) the 

 corpus callosum, described on page 934; (b) the anterior commissure, described on 

 page 947; and (c) the hippocampal commissure, described on page 945. 



