426 SPECIAL HISTOLOGY. 



the olivary body; 2. in the restiform bodies, the grey 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 lateralis, but also 

 extends into the fasciculi cuneatus and gracilis. This struc- 

 ture may be described as a continuation of the posterior horns 

 of the spinal-cord, even presenting, as Stilling correctly states, 

 an indication of the substantia gelatinosa of those processes, of 

 which it may moreover be observed, that it is very remarkably 

 developed in the uppermost portions of the cord, as far as the 

 commencement of the decussation of the pyramids, and has a 

 position entirely lateral. The elements of the grey 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 

 grey substance on the floor of the fourth ventricle, is the con- 

 tinuation of the grey 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, nume- 

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

 0-006'", or even O008'", in part of the finer and finest kinds, 

 and besides these, nothing but caudate nerve-cells of all 

 dimensions from O006'", up to 003'", and more. The 

 largest of these are contained in the ala cinerea at the posterior 

 extremity of the fourth ventricle, 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 grey 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 gre}^ substance, 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 pyra- 

 mids near the olivary bodies, and in the olivary columns, 

 external 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 mnrh 



