382 OEIGiyAL AETICLES. 



substantia gelatinosa of the caput cornu posterioris are considered by 

 Clarke as belonging to tlie connective tissue. The outer ends of the 

 epithelial cells which surround the central canal send out delicate 

 processes which radiate in all directions, and by their peripheral 

 ends are always in connection with the areolar or connective tissue. 

 Some processes may be traced to the blood-vessels and pia mater 

 through the grey substance and columns, at right angles to the axis 

 of the cord, joining the connective tissue. We have ourselves seen 

 this connection of the epithelial cells of the canal -^-ith the pia mater 

 of the anterior fissure, in a beautiful preparation by IVIr. Lockhart 

 Clarke, of the cord of a foetus of a sheep three inches only in length 

 — leaving no longer any possibility of doubt on the existence of the 

 connection. 



Dean* observes — " My own observations are entirely in agree- 

 ment with the description which J. L. Clarke has given of the con- 

 nective tissue." " Tlie view which Clarke has taken of the possible 

 relation between connective and true nerse tissue seems very valuable ; 

 for I have long been satisfied of the impossibility of fully distinguish- 

 ing with our present means, between these two tissues, which seem 

 to run into each other so closely as to suggest very strongly the im- 

 portant question, whether there is any actual and essential difier- 

 ence between them, or whether the connective tissue of the cord be 

 intermediate in its natm-e, passing on the one hand into nerve tissue, 

 and on the other into pia mater." 



Groll (p. 136) describes the interstitial substance or Neuroglia of 

 the white columns as being identical with the finest fibres, forming 

 the sheaths of the nerve fibres, and as continuous throughout the 

 entire length of the spinal cord. This is also shown by Mr. Clarke, 

 Phil. Trans, pi. xxii. fig. 48. At the edges of very thin sections Goll has 

 seen the short sections of axis cylinders fallen out, leaving a honey- 

 comb structure distinctly perceptible. At the borders of the anterior 

 fissure this neuroglia is continuous, with a fine fibrdlated texture, 

 which is interposed between the white column and the pia mater. 



n. FOEM AITD StEIICTTJEE OF THE GrEET SrBSTAIfCE. 



1. Form. The general outlines of the grey matter are well known, 

 as are also its division into anterior and posterior horns. It may be no- 

 ticed that these outlines are not so clearly defined as the cord tapers 

 towards its lower extremity. At the lower part of the conus medul- 

 laris, or conical extremity, the posterior grey substance forms a single 

 broad mass, consisting behind of a softer, paler and more transparent 

 lamina or baud (the gelatinous substance). The anterior portion of 

 the grey substance of the conus, however, retains more of the form of 

 the cornua, being divided into two parts by the anterior fissure, near 

 the base of which fibres are seen crossing and decussating to form the 



* P. 2. 



