360 SPECIAL HISTOLOGY. 



clusively of nerve-fibres, whilst the gray nuclear portion with its pro- 

 longations, the cornua, or horns, is formed, in almost equal proportions, 

 of nerve- fibres and cells. 



The white substance of the spinal cord may, for the purpose of de- 

 scription, be most conveniently, and in accordance with usage, divided 

 into two halves, and each of these into three columns. The anterior 

 columns (funiculi anteriores), are, towards the interior, almost com- 

 pletely separated from each other by the anterior fissure (fissura ante- 

 rior), which extends the whole length of the cord, and into which a 

 vascular process of the pia mater penetrates. At the bottom of the 

 fissure, however, the columns are united by the anterior or white com- 

 missure (com. alba)', externally, they extend as far as the points of exit 

 of the anterior roots of the nerves, or to the sulcus lateralis anterior, 

 but are here inseparably connected with the lateral columns (funiculi 

 laterales), which again, at the points of exit of the posterior roots, where 

 the sulcus lateralis posterior is situate, are continuous, without any line 

 of demarcation, with the posterior columns. The latter (funiculi pos- 

 teriores) appear indeed as if they were in contact in the posterior mesial 

 line, because the posterior longitudinal fissure described by many anato- 

 mists, does not exist in man, except in the lumbar enlargement of the 

 cord, and in the superior cervical region ; but they are nevertheless 

 separated, to such a degree, throughout the whole length of the cord 

 by very numerous vessels, which in the posterior mesial line penetrate 

 as far as the gray nuclear portion, that the columns in most places are 

 not even in contact, and even where they are, they are merely in juxta- 

 position, and never by any means continuous into each other. Thus 

 the white substance of the cord represents two halves, united only by 

 the anterior white commissure, and each of which is divided more arti- 

 ficially into three columns, which occupy the depressions left between 

 the projecting processes of the gray substance. 



The gray substance presents a central portion, more of a riband-like 

 form, and four laminae projecting laterally from it, so that its transverse 

 section forms a cross. The central portion or the gray commissure, in 

 the adult, does not, normally, contain any canal, such as exists in the 

 foetus, and consists of a central, cylindrical, or flattened tract, consti- 

 tuted principally of nerve-cells, of a yellowish color the gray nucleus 

 (subst. grisea. centralis), and of nerve-fibres running transversely, con- 

 tinued beyond the nucleus, before and behind it the gray or posterior 

 commissures. Of the laminae, in a transverse section also termed horns, 

 the anterior are thicker, and shorter, of a uniform gray color, composed 

 of larger and smaller nerve-cells, and of delicate nerve-fibres of me- 

 dium fineness; the posterior, longer and thinner, are constituted at 

 their roots like the former, only most usually of smaller cells; but at 

 the free edge are invested with a more transparent layer, containing 



