FISSURES OF THE SPINAL MARROW. 561 



lum. The contrast of color between the two substances is the more 

 marked, the younger the subject upon which the examination 

 is made. In old age the contrast ceases to be distinct ; the 

 central nucleus of the medulla presents but a grayish tint, 

 yellowish at its border where it unites with the medullary 

 matter, which has likewise become of a yellowish color. 

 — The shape of the cineritious nucleus of the medulla spinalis, 

 is in most parts like that of two )— ( united thus back to back ; 

 in others it presents the appearance of four bands of cineritious 

 matter, one anterior and one posterior to each half of the 

 medulla. 



— These four bands, or the two c' are very generally united 

 together in the centre of the medulla, though Keuffel, has 

 found those of each side entirely separate. The anterior horns 

 or bands, do not quite reach the surface of the cord, but are 

 exactly opposite the connexion of the anterior roots of the 

 nerves with the spine. The posterior extend completely 

 through its substance, at the point where the posterior roots are 

 connected with the cord. The bulk of the cineritious matter 

 is always larger, where the largest amount of nerves are 

 connected with the medulla, as in the brachial and lumbo- 

 sacral plexus. It is also relatively to the white neurine, 

 larger in man than in any other animal. The anterior horns 

 of the cineritious matter, are not so long, but are thicker than 

 the posterior. 



— The anterior and posterior median fissures do not quite 

 extend into the cineritious nucleus ; the bottom of the fissures 

 is closed by a layer of white matter, which is evidently trans- 

 verse in the anterior, and, as I have repeatedly seen, is 

 formed of a sort of medullary pellicle arising from the anterior 

 part of each half of the cord, so as to form a union or commis- 

 sure between the two halves. The posterior fissure is closed in 

 a similar way, notwithstanding the assertion of Gall and Spur- 

 zheim that the fibres of the posterior commissure were longitudi- 

 nal in their directions. The longitudinal appearance of the fibres 

 observed by these anatomists is made by the tearing up of the 

 vessels in removing the pia mater. Each of these transverse 



