INTEENAL STRUCTUEE. 



557 



within the gyrus to which they belong, and are connected with the ante- 

 rior perforated space, being joined by certain longitudinal fibres which 

 run along the under surface of the corpus callosum near the middle line,, 

 passing near and upon the upper edge of the septum lucidum. Behind,, 

 they turn round the back of the corpus callosum and thence descend ta 

 the point of the middle lobe, where, according to Foville, they again 

 reach the perforated space. Offsets from these fibres pass upwards and 

 backwards into the secondary convolutions derived from the gyrus 

 fornicatus in the longitudinal fissure. 



1). Fasciculus vncinalus. — Under this name is described a white 

 bundle, seen on the lower aspect of the hemisphere, passing across the 

 bottom of the Sylvian fissure, and connecting the frontal with the 

 temporo-sphenoidal lobe (fig. 388, e). The fibres of this bundle expand 

 at each extremity, and the more superficial of them are curved or 

 hooked sharply between the contiguous parts of the anterior and middle 

 lobes, — whence it has derived its name. 



c. The convolutions of the cerebrum are connected with each other 

 by white fibres, which lie immediately beneath the cortical substance. 

 Some of them pass across the bottom of the sulcus between adjacent 

 convolutions ; whilst others, which are longer and run deeper, connect 

 convolutions situated at a greater distance from one another. 



Fig. 389. 



Fig. 389. — View op a Dissection of the Fibres of the Gyrus Fornicatus and Fornix, 

 IN the PiIght Hemisphere (slightly altered from Foville). h 

 A, the anterior lobe ; B, the posterior lobe ; a, a', a", fibres of the gjTus fomicatus ; 

 c, c', oblique bands of fibres of some of its accessory gyri ; b, tegmentum, and g, crust of 

 the crus cerebri, separated by the locus niger ; I, thalamus ; m, fissure of Sylvius ; n, corpus 

 albicans ; q, median section of the corpus callosum ; s, septum lucidum ; t, the foi-nix, 

 its anterior pillar descending into the corpus albicans, and then emerging from that at its 

 termination (*) in the thalamus ; 1, the olfactory bulb ; 2, the optic commissure. 



!Foville's Views. — Tlie researches of Foville have led him to differ con- 

 siderably from other anatomists as to the course of the fibres of the cerebrum, 

 as will be seen from the following statement of his views. 



1. The crufit ov fusriculatcd j'orttoti of each cerebral peduncle, derived from 

 the anterior pj-ramid, forms by itself the peduncular fibrous cone, and is thence 

 continued on into the radiating fibres of the ceiel'rum, which are destined only 

 for the convolutions on the convex sui-face of the hemisphere, including the outer 

 half of the marginal convolution of the longitudinal fissm-e, and the inner half 

 of the convolution around the Sylvian fissui'e. 



