442 THE BRAIN OF MAMMALS, BY TH. MEYNERT. 



closed between it and the corpus geniculatum (fig. 249, Bs, 

 Ge, Gi\ 



The brachia of the corpora quadrigemina terminate, perhaps 

 like all the remaining fasciculi of the corona radiata, in the 

 ganglion of the hemisphere of their own side. The median 

 decussation lies on the other side of their interruption by 

 means of the cells of the corpora quadrigemina, and belongs 

 to the fasciculi of the crus cerebri after their origin from the 

 mass of the corpora quadrigemina. 



No doubt can exist respecting these relations of the brachia 

 of the corpora quadrigemina so far as regards the deeper-lying 

 fasciculi directly penetrating the ganglion substance ; but we 

 may also with certainty make the same assertion as to the 

 fasciculi of the brachia that in the first place help to form 

 the medullary investment of the corpora quadrigemina, be- 

 cause the cells of the nates and testes not only belong to the 

 grey matter of the nuclei, but are freely interspersed also 

 through the most external layers of the zonular layer, so that 

 these fasciculi of the corona radiata are by no means obliged to 

 penetrate into the interior of the opposite nucleus in order to 

 reach their terminal cells. The relation of the most anterior 

 fasciculi of the brachia of the nates to the decussation is less ob- 

 vious ; for these in transverse sections of the brains of Monkeys 

 perforate the thalamus opticus in very loose arrangement, whilst 

 in traversing the nates they form a very compact fasciculus. 

 Nevertheless it is probable that the above-named, and still to be 

 more minutely described, fasciculi terminate in the ganglion of 

 the corpora quadrigemina of the same side, inasmuch as they 

 curve round to the middle line, and may run backwards in 

 order then first to decussate. The course of the fasciculi finely 

 distributed through the grey substance which in longitudinal 

 sections may be seen running through the superior pair of the 

 corpora quadrigemina, and which extend from the entrance of the 

 brachia of the nates to points situated far behind in the median 

 decussation, is in accordance with this supposition (fig. 241, Q'). 



It has already been stated that fasciculi from the tractus 

 opticus are associated with the brachium of the inferior pair of 

 the corpora quadrigemina whilst it is invested by the internal 

 corpora geniculata. 



