THE CEREBRUM 



425 



upper surface of the corpus callosum is coated by an exceed- 

 ingly thin layer of grey matter, called the indusium griseum^ 

 which is continuous, at the bottom of the callosal sulcus, with 

 the grey cortex of the hemisphere. Associated with the 

 indusium, on each side of the median plane, are two delicate 

 longitudinal bands of fibres called the striae longitudinales 

 rnedialis and lateralis. The stria longitudinals medialis is the 

 more strongly marked of the two, and it is separated from 

 its fellow of the opposite side by a faint median furrow. 

 The stria longitudinalis lateralis is placed more laterally. So 



Genu of 



Olfactory tract-J 



Optic chiasma 

 thrown back 



Lamina terminalis 

 Gyrus subcallosus 



FIG. 162. Anterior end of the Corpus Callosum and the Subcallosal Gyri 

 as seen from below when the frontal lobes of the hemispheres are 

 slightly separated from each other. (From Cruveilhier. ) 



thin is the indusium that the transverse direction of the 

 bundles of callosal fibres can be easily seen through it. 



The strioe, with the thin layer of grey matter associated with them, 

 represent a gyrus called the gyrus supracallosus. 



The two extremities of the corpus callosum (Fig. 160) are 

 greatly thickened, whilst the middle part, the truncus (O.T. 

 body), is considerably thinner. The thick posterior end, 

 which is full and rounded, lies over the mesencephalon, and 

 extends backwards as far as the highest point of the cerebellum. 

 It is called the spknium. The anterior end, which is less 

 thick than the posterior, is folded, downwards and backwards, 

 upon itself, and is called the genu. The recurved lower 



