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of the median furrow increases gradually in depth, and includes the 

 substantia ferruyinea. It is developed in the tract which is con- 

 tinuous with the nucleus of the hypoglossal nerve, of which it is the 

 analogue. Anteriorly, on each side of the raphe, there is gradually 

 developed within it a considerable group of large multipolar cells, 

 which becomes the nucleus of the third cerebral nerve. At its 

 outer and back part it adjoins the tract which forms the side wall of 

 the ventricle, is continuous with the auditory nucleus, and lies at 

 the base of the caput cornu posterioris. This latter tract, on reach- 

 ing the corpora quadrigemina, becomes continuous with its fellow 

 of the opposite side to form the roof of the iter a tertio ad quartum 

 ventriculum. Here it becomes gradually broader and more trans- 

 parent, and, in the form of an arched lamina, supports the lateral 

 lobes of the corpora quadrigemina, with which, at its border, it is 

 intimately blended, and which communicate over it by a transverse 

 band of fibres. It contains a multitude of small cells of various 

 shape and size, and is interlaced in every direction by very fine 

 nerve-fibres ; but of the latter there are two regular sets, which run 

 longitudinally and transversely, and which increase in number from 

 behind forwards, so that they are much more numerous beneath the 

 nates ; the transverse fibres radiate in straight lines towards the 

 surface through the lobes of the corpora quadrigemina. 



Structure of the Corpora Quadrigemina. The lateral lobe of each 

 testis is an oval or almond-shaped mass, which rests on the convexity 

 of the transparent arch just described. It contains a considerable 

 number of small and uniformly scattered cells of various shapes, and 

 of an average size of about the 2400th of an inch, together with 

 oblique, transverse, and longitudinal nerve-fibres ; the longitudinal 

 fibres form a denser layer at its inner and still more at its outer side. 

 The transverse fibres form two sets, one extending over the arched 

 lamina to the opposite lobe, and derived chiefly from the fillet ; the 

 other radiating, as already stated, from the substance of this lamina 

 beneath, towards the surface, and becoming continuous, at least in 

 part, with the first set, as well as with the longitudinal. 



The structure of the nates is, in general, similar to that of the 

 testes : their cells are nearly of the same nature, but smaller ; their 

 lobes are shallower, but longer ; and the arched transparent lamina 

 on which they rest is broader and more transparent. Both the trans- 



2D2 



