426 THE BRAIN 



portion of the anterior part of the corpus callosum rapidly 

 thins as it passes backwards, and is termed the rostrum. 

 The fine terminal edge of the rostrum is connected with the 

 lamina terminalis (Fig. 160). 



Both the lateral and the medial longitudinal striae and the 

 indusium, which lie upon the upper surface of the corpus 

 callosum, turn downwards, round the splenium, and become 

 continuous, below it, with the attenuated posterior part of the 

 hippocampus, a structure which will be seen, later, in the 

 inferior horn of the lateral ventricle. Immediately above the 

 union of the indusium with the hippocampus there is a 

 narrow ridge of grey matter, called the fasciola cinerea, which 

 is the posterior, terminal part of the fascia dentata (Fig. 

 156). Anteriorly, the striae and the indusium pass round the 

 genu, and then along the under surface of the rostrum until 

 they terminate in the gyrus subcallosus of the corresponding 

 side. The gyrus subcallosus is a ridge which descends from 

 the rostrum of the corpus callosum and passes towards the 

 medial olfactory stria and the substantia perforata anterior 

 (Fig. 1 60). 



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 carports callosi. The more anterior of the 

 fibres which compose the genu of the corpus callosum sweep forwards, 

 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 backwards 

 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. The tapetum is a thin layer, of 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 6 mm. (a quarter of an inch) or less 

 from the median plane, on each side. The central portion of 

 the corpus callosum which lies between the incisions is to 



