TTIE NERVOUS SYSTEM. 



427 



as 0-Q25'"), and finer nerve-tubes. One part of the grey sub- 

 stance just described, that namely of the anterior half of the 



Kg. 117. 



fourth ventricle, belongs properly to the pons Varolii, It also 

 contains, in its interior, besides the just described elemeuts, 

 above the transverse fibre-layer, both in the middle as well as 

 more laterally, many accumulations of grey substance, with 

 larger and smaller (as much as O02'" and more) nerve-cells, all 

 caudate, which are so irregularly imbedded among the longi- 

 tudinal and transverse fibres, as to require no detailed descrip- 

 tion, and are connected on the one side with the grey nuclei 

 of the medulla oblongata, and on the other with the substantia 

 nigra of the crura cerebri. 



The relations of the ten pairs of nerves which arise from the 

 medulla oblongata, the pons, and the crura, constitute a very 

 difficult question. But few inquirers have endeavoured to 

 solve it by other means than those usually employed, that is 

 to say, by the tracing of the fibres, with the aid of the scalpel, 



Fig. 1-17. Nerve-cells of the substantia forruyinea in the floor of the fourth ven- 

 tricle or rhomboid fossa, of Man, x 350 iliatn. 



