-154 ME. J. L. CLAKKE OX THE GEEY SUBSTAXCE OF THE SPIXAL COED. 
terminale, it rises to the surface in the middle line and extends directly across (see fig. 20. 
Plate XXIII.); meanwhile the posterior columns [K, A) become gradually shallower and 
at length disappear, excejpt at the sides, so that the gelatinous sulstance behind is covered 
only by the pia mater (m) of the cord, with which it is immediately connected. The deep 
posterior strata of the lateral columns obliterate it at the sides, by encroaching in bundles 
on the grey substance which forms a continuous network around them. Still lower down 
(see fig. 21, Plate XXIII.) the canal is prolonged backwards as far as the gelatinous sub- 
stance, and dilates in a lateral direction behind the dark bundles (D), which in the pre- 
ceding sections occupied the interior of each caput cornu, (See explanation of Plates.) 
In Mammalia a series of nearly similar changes may be observed, except that the 
posterior columns are not interrupted in the middle line. 
Fig. 22, Plate XXIV. represents a transverse section of the conus rnedullaris of the 
Ox, near the third pair of coccygeal nerves, magnified 60 diameters. Multitudes of fibres 
are observed to radiate from the grey substance and form a beautiful network through 
the white columns. From the extremities of the anterior cornua considerable offsets of 
the grey substance are prolonged through the anterior columns, rejoining each other 
around masses of longitudinal fibres, and reaching the surface to be continuous Muth the 
layer of connective tissue. Amongst these offsets, and even in the masses of longitudinal 
fibres, several large cells are scattered very nearly to the surface of the cord ; some of 
their processes appear to reach the connective tissue at the surface. 
Through the lower part of the conus rnedullaris the canal continues to enlarge. It 
nearly reaches the anterior fissure, and extends backwards to the gelatinous substance, in 
front of which it dilates in a lateral direction (see fig. 23, Plate XXIV.). The grey sub- 
stance, as it descends through the cemus, gradually decreases in quantity, and is encroached 
upon more and more by the antero-lateral columns, around the bundles of which it 
radiates outwards as a network. Numerous small oval and fusiform cells, with one or 
two others of superior size, are scattered through it. The filum terminate, in its natural 
state, appears to be a nearly cylindrical tubule, but, when hardened in spirit or chromic 
acid, is more or less flattened at the sides, so that the canal becomes compressed and 
sometimes completely collapsed (see figs. 24 & 25, Plate XXIV.). The grey substance is 
at length reduced to a mere border or fringe (fig. 25), from the edges of which a series 
of tapering processes (a, a) extend through the white substance to the pia mater at tlie 
surface. The larger kind of cells have entirely disappeared, but a number of small 
fusiform cells, or nuclei, resembling those of the connective tissue, are observed in con- 
tinuity with fibres which run along it and form arches from one process of the grey 
substance to another, as they pass out to the white columns. 
them (“ Clarke’s Preparatious-metliode zeigte ilim aber beide Substauzeu zu bell, als dass er eiueiiHuter- 
scbied hiitte huden kouneu”); but, if he liad taken the trovible to read the explanation of tlie figure in 
(question, he would liave seen that it was drawn from a section of the conus rnedullaris, treated o«/y hi/ 
acetic acid. The continuity of the gelatinous substance is so apparent at this part, both in a fresh state 
and when hardened with chromic acid, that Stilling’s denial of the fact seems to me unaccountable. 
