THE CEREBRUM 483 



downwards, round the splenium, and end in the fasdola 

 cinerea. The fasciola cinerea, which is situated immediately 

 beneath the splenium, is a narrow strip of grey matter, 

 continuous posteriorly with the medial and lateral striae 

 of the same side and anteriorly with the fascia dentata 

 hippocampi. Anteriorly, the striae pass round the genu, and 

 then along the under surface of the rostrum until they 

 terminate in the corresponding gyrus subcallosus. The gyrus 

 subcallosus is a ridge which descends from the rostrum of the 

 corpus callosum and passes to the surface of the substantia 

 perforata anterior. There the fibres of the striae contained 

 in the gyrus emerge from its substance, and pass postero- 

 laterally along the posterior limit of the substantia perforata 

 anterior towards the anterior extremity of the temporal lobe. 



Fibres of the Corpus Callosum. The transverse fibres of the corpus 

 callosum, as they enter the white medullary centre of the cerebral hemisphere, 

 radiate from each other towards various parts of the cerebral cortex. This 

 radiation is called the radiatio corporis callosi. The more anterior of the 

 fibres which compose the genu of the corpus callosum sweep anteriorly 

 in a series of curves towards the frontal pole of the hemisphere. They 

 form the forceps minor. A large part of the splenium, forming a solid 

 bundle termed the forceps major, bends suddenly and abruptly posteriorly 

 into the occipital lobe. Fibres from the trunk of the corpus callosum and 

 also from the splenium curve round the lateral ventricle and form a very 

 definite stratum called the tapetum. This is a thin layer in the medullary 

 centre of the hemisphere which forms the roof and lateral wall of the 

 posterior horn and the lateral wall of the posterior part of the inferior horn 

 of the lateral ventricle. 



VENTRICULUS LATERALIS. 



The lateral ventricle, in the interior of the cerebral hemi- 

 sphere, should now be opened up on each side. The corpus 

 callosum, which forms the roof of the central part (O.T. body) 

 and anterior horn of this cavity, must, therefore, be partially 

 removed. 



Dissection, Make a longitudinal incision, through the corpus callosum, 

 about a quarter of an inch from the median plane on each side. The central 

 portion of the corpus callosum which lies between these incisions is to be 

 kept in position. The lateral portions must be turned laterally and 

 detached completely. As this is being done, it will become evident that the 

 lower part of the splenium which is prolonged into the forceps major is in 

 reality a portion folded anteriorly in close apposition with the under surface 

 of the posterior end of the corpus callosum. Be careful to leave the forceps 

 major in its place. 



The central part and the anterior horn of the ventricle are now exposed ; 

 but the cavity of the ventricle runs posteriorly into the occipital lobe in 

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