ORGANS OF THE BODY. 595 



of fibres further springs from the external border of the thalamus. As 

 to the histology of the part, we possess but very little satisfactory informa- 

 tion. Cells are to be found here which appear to differ from the large 

 multipolar elements, most of them being fusiform. The pulvinar presents 

 nothing remarkable about it. In the external geniculate body the cells 

 are frequently pigmented ; the internal contains fusiform elements. 



We pass on now to the corpora atriata and nucleus dentatus. 



Both these present a grey surface. In them terminate fibres from the 

 bases of the crura cerebri. Externally, both ganglia send fibres tp the corona 

 radiata (Stabkranz). The grey matter of both ganglia presents for the most 

 part great uniformity of structure. In it we meet with larger and smaller 

 multipolar ganglion cells and small elements, measuring '005-0 '01 mm. 

 The neuroglia is similar here to that in the cortex of the cerebrum. 



In respect to the nuclei amygdalce and claustrum we are in want of 

 trustworthy observations. 



Turning now to the coronata radiata, we find that it consists in 

 the first place of fibres which, without having touched one of those 

 ganglia, ascend directly through the crura cerebri, and then of the radia- 

 tions of the ganglionic masses. These great masses of fibres are probably 

 connected with the intellectual functions. 



The corpus callosum, on the other hand, has nothing to do either with 

 the peduncles of the brain or the corona radiata. ]t is a purely commis- 

 surai system of fibres, radiating extensively in the hemispheres of the 

 cerebrum, as also is the anterior commissure. Besides these, there are 

 well developed systems of fibres which connect various parts of the brain 

 on the same side, as, for instance, the fibres of the surface which unite 

 the gyri one with the other "associating fibres." 



The white substance of the hemispheres consists of medullated fibres of 

 about 0'0026-0'0067 mm. in diameter. At the surface only of the larger 

 ganglionic masses, and towards the cortex is the non-medullated species 

 to be found. 



The nerve-fibres are grouped together in bundles invested with a cover- 

 ing of connective-tissue cells (Gfolgi, Soil). 



The cortex of the hemispheres may be divided into several layers, not 

 distinctly marked off, however, against one another at all points. Their 

 number, also, has been variously estimated by several observers, among 

 whom may be mentioned Koelliker, Stephany, Berlin, Arndt, Meynert, 

 Henle, and Stieda. This is easily conceivable, and it is probable that it 

 varies also in the different lower mammals. 



We regard the cortex in man as divisible into six laminae, but would 

 mention that our material has been in the last few years very insufficient. 

 We were unable to procure brains fresh enough for our object. 



(1.) The uppermost layer (Koelliker) consists of a series of horizontal 

 transverse and oblique fibres, probably of nervous nature. 



(2.) The next the first, of Meynert (fig. 562, ]), is among the mam- 

 mals deeper than in man, and is composed chiefly of neuroglia with a few 

 scattered nervous elements. Two forms of the latter have been described 

 in the first place, namely, small cells of '009-0 '010 mm. in diameter, 

 and of polygonal or pyramidal figure giving off processes ; and secondly, 

 networks of the most delicate nervous fibrillse of unknown nature. 



(3.) A layer of crowded small multipolar nerve cells usually of pyra- 

 midal form (2). 



(4.) A deep stratum in which much larger many-rayed ganglion cells, 



