448 THE BRAIN OF MAMMALS, BY TH. MEYNERT. 



The cells from which each fasciculus of the fifth nerve 

 arises, present instructive points of difference from those that 

 are found in the nucleus common to the third and fourth 

 nerves. The former resemble distended vesicles, possess but 

 few and delicate processes that are given off abruptly like a 

 soap-bubble still hanging from a straw. The latter are also 

 large but slender, with numerous processes which gradually 

 become attenuated from their base outwards. The former re- 

 semble the cells of the interspinal ganglia, the latter those of 

 the anterior cornua of the spinal cord. The typical forms 

 of the cells of origin of the sensory and motor nerves thus 

 exhibit no striking contrast in regard to their size, though 

 they are characterized by certain well-defined morphological 

 differences. 



In Mammals a remarkably distinct dark line extends from the 

 median furrow of the corpora quadrigemina to the upper border of 

 the epithelium of the aqueduct, forming a kind of raphe, which, in 

 the Cat, I have been able to recognize as a median lamina of fibrous 

 connective tissue containing bloodvessels, and which at the posterior 

 margin of the canal divides in a manner exactly similar to the process 

 of connective tissue occupying the posterior fissure of the spinal cord, 

 and towards which extend the fibrillated extremities of the posterior 

 epithelial cells. In Dogs I have seen in this lamella oblong and stellate 

 cells ; in Man this dark line is also perceptible, and is most distinct at 

 the level of the testes. 



Of the ganglia of the corpora quadrigemina, that of the 

 anterior pair, or nates, appears in transverse section on each 

 side in the form of a plano-convex lens, the base resting on those 

 fasciculi of the crus cerebri which proceed outwards and for- 

 wards from the median decussation ; those of the inferior pair, 

 or testes, are delicate bi-convex but sharply defined lenses, 

 the inferior borders of which, again, are circumscribed by the 

 innermost fasciculi of the portion of the crus cerebri proceeding 

 from them. 



The nerve cells in the corpora quadrigemina exhibit re- 

 markable variations in size. As a general rule, the smaller 

 forms, having a length of from 15 to 21 ju, and a breadth of 5 /LI, 

 predominate, and such are found exclusively in the most super- 



