21 8 NERVOUS SYSTEM. [SECT. III. 



does not appear to me, however, a sufficient reason for denying its existence ; 

 and I believe that here, as in the case of the finest nerve-tubes, we must 

 abstain, for the present, from giving a definite opinion. 



Within the last year, Stilling has described a very complicated structure 

 in the nerve-cells and nervous fibres, viz., anastomosing small tubuli occurring 

 in great numbers in all parts of these elements. I for my part cannot lay 

 great stress upon the assertion of this author, inasmuch as his observations 

 have been made on chromic acid preparations, and because he gives no proof 

 whatever that the pretended tubuli are really such. 



Central Nervous System. 



§ hi. Spinal Marrow. — The nervous elements in the spinal 

 marrow are so distributed, that the external white substance is 

 exclusively formed of nerve-tubes ; the grey centre, with its pro- 

 cesses or cornua, on the other hand, of nerve-tubes and nerve- cells, 

 in almost equal proportion. 



The white substance of the spinal marrow may, for convenience 

 of description, be divided in the customary manner into two halves, 

 and each of these into three columns. The anterior columns are 

 almost completely separated from each other by the anterior fissure 

 which extends along the whole length of the cord, and into which 

 a vascular process of the pia mater dips, but are still connected at 

 the bottom of the fissure by the anterior or white commissure. 

 They extend outwardly to the place of exit of the anterior roots, 

 or to the sulcus lateralis anterior, but are here, however, insepa- 

 rably connected with the lateral cords r which, in like manner, at 

 the place of exit of the posterior roots, where the sulcus lateralis 

 posterior is situate, pass into the posterior cords without any line 

 of demarcation. These posterior cords apparently meet, it is true, 

 in the posterior median line, inasmuch as the posterior fissure 

 assumed by many does not exist in man, except in the lumbar 

 enlargement and the upper cervical region ; but they are so sepa- 

 rated from each other, in the entire extent of the cord, by very 

 numerous vessels and connective tissue, which, in the posterior 

 median line, penetrate as far as the grey central part, that their, 

 elements do not, in most places, come in contact at all, and 

 Avhere this is the case, are only in juxtaposition, and never pass 

 from one side to the other. The whole substance of the cord, 

 accordingly, exhibits two halves, united only by the anterior white 

 commissure, each of which may be divided more artificially into 

 three columns, which fill up the depressions existing between the 

 projections of the grey substance. 



The grey substance possesses a middle ribbon-shaped portion 

 and four laminae, proceeding from it laterally, so that, when viewed 



