THE NERVOUS SYSTEM. 375 



closest observation has failed to afford me any indication of a connection 

 between these cells and the fibres which run among them. On a level 

 with the two upper thirds of the olivary body, is placed, behind the 

 nucleus and wholly isolated from it, the body termed by Stilling the 

 accessory olivary nucleus, in the form of a flattened, yellowish band, of 

 exactly the same structure as the gray substance of the olivary body, 

 and also traversed by horizontal nerve-fibres, and in fact by fibres which 

 have for the most part already passed through the olivary body ; 2, in 

 the restiform bodies, the gray substance {corpus s. nucleus cinereus) 

 assumes the form of an ill-defined, elongated mass intermixed with very 

 numerous nerve-fibres, and which occupies mainly the fasciculus late- 

 ralis, but also extends into the fasciculi cuneatus and gracilis. This 

 structure may be described as a continuation of the posterior horns of 

 the spinal cord, even presenting, as Stilling correctly states, an indi- 

 cation of the substantia gelatinosa of those processes, of which it may 

 moreover be observed, that it is very remarkably developed in the upper- 

 most portions of the cord, as far as the commencement of the decussa- 

 tion of the pyramids, and has a position entirely lateral. The elements 

 of the gray substance of the restiform bodies are, besides, numerous 

 finer fibres, which appear to pass chiefly into the horizontal, internal 

 fibre-system, and many, rather pale, but in part brownish nerve-cells 

 with processes, pretty regularly disposed, and most of them of the same 

 size as those of the olivary bodies ; 3, the gray substance on i\\e floor of 

 the fourth ventricle, is the continuation of the gray nucleus of the spinal 

 cord, and forms a tolerably thick layer, extending from the calamus 

 scriptorius as far as the aqueductus Sylvii. It contains throughout, 

 numerous nerve-fibres, in part of very considerable diameter, up to 

 0-006, or even 0-008 of a line, in part of the finer and finest kinds, and 

 besides these, nothing but caudate nerve-cells of all dimensions from 

 0-006, up to 0-03 of a line, and more. The largest of these are con- 

 tained in the ala cinerea at the posterior extremity of the fourth ventri- 

 cle, and in the subst. ferruginea s. locus cinereus (Fig. 147), in which 

 latter situation, the cells also present well-marked pigmentary matter, 

 and very numerous, delicately branched processes. The small multi- 

 nuclear cells, which in the gray nucleus of the cord occur in the form of 

 a compact structure, are here entirely wanting, not being found beyond 

 the decussatio pyramidum. Besides these three masses of gray sub- 

 stance, which can in part be referred to that of the spinal cord, there 

 are found, in the medulla oblongata, some small collections of it, as in 

 the pyramids near the olivary bodies, and in the olivary columns, exter- 

 nal to the accessory nucleus, in all of which, as has been already stated 

 by Stilling, are also to be seen in part larger cells, all caudate (in the 

 latter situation measuring as much as 0-025 of a line), and finer nerve- 

 tubes. One part of the gray substance just described, that namely of 



