STRUCTUKE OF THE LOBES OF THE CEREBRUM. 405 



callosum, and known as the nerves of Lanoisi, which are poste- 

 riorly continuous with the substantia reticularis and nuclear 

 layer of the cornu Ammonis, and anteriorly with the grey 

 substance of the internal olfactory convolution. Moreover the 

 internal surface of the septum pellucidum is covered by longi- 

 tudinal fasciculi which arise from the internal olfactory convo- 

 lution, and emerging from it partly penetrate the genu of the 

 corpus callosum, and partly run beneath, it, traversing the body 

 and splenium to enter every part of the course of the gyrus 

 fornicatus. They perhaps unite with the parallel fusiform cells 

 of the septum (fig 241, L, fit ', + + +, m, Bl P). 



The superficial and the deep-seated medulla of the external 

 olfactory convolution coalesces on the one hand with the sub- 

 stantia reticularis of the uncinate convolution (fig. 242, m, ret), 

 on the other hand with the proper medullary fold of this 

 body, which forms a moderate-sized lamina between the cor- 

 tex of the hook (uncinus), and the nucleus of the amygdala 

 (fig. 242, m* + m/). In this way a process of the claustrum 

 grows into the medulla of the external olfactory convolution, 

 through the fusiform cells of which it enters into connection 

 with the wide-spreading connecting system of the Sylvian 

 fissure (fig. 242, m' CZ). 



In regard to the system of the corpus callosum, the micro- 

 scopic investigation of transverse sections of the cerebrum of 

 small animals, and that of the Bat in particular, which last has 

 been carefully studied by Oellacher, demonstrates the truth of 

 the statement made by Arnold, that the system of the corpus 

 callosum consists exclusively of commissural fibres between 

 corresponding and identical regions of the opposite sides of the 

 cortex, and not, as Foville maintained, of decussating fasciculi 

 of the projection system entering into the ganglia. It can also 

 be shown that it does not, as Burdach believed, pass to any 

 special convolution, but is, along with the projection system, 

 distributed to all. Hence, as stated by Arnold and Reichert, 

 the fasciculi of the corpus callosum and the projection fasciculi 

 decussate in various directions. The splenium of the corpus 

 callosum, in consequence of its inferior reflection, presents 

 two layers (fig. 241), not a solid mass, the two laminae of which 

 permit the fissure of posterior and descending cornua to occur 



