CHORD, WITH FURTHER INVESTIGATIONS INTO ITS STRUCTURE. 
349 
down the chord, sends forwards, at short intervals, into the anterior grey substance, 
a series of fibres like those issuing from the roots of plants. In this longitudinal 
course it is joined by corresponding fibres from bundles above and below it, which 
thus contribute to form a continuous band. 
The fibres projecting from this band into the anterior grey substance have the 
following distribution. Part of them form loops with each other within the grey 
substance, particularly near its border; others extend directly into the anterior white 
columns A, C, and bending round both upwards and downwards, are seen sometimes 
to re-enter the grey substance and form with each other a series of loops, and some- 
times to continue a longitudinal course within the anterior white columns, amongst 
the fibres of which they become lost. Whether the latter, also, ultimately form 
broader loops with corresponding fibres from the grey substance, it is impossible to 
ascertain. But even if those which ascend in the anterior columns are continued 
upwards to the brain, one can scarcely avoid inferring that those which descend 
re-enter the grey substance, either to form loops, or to become continuous with the 
fibres of the anterior roots, since the whole of the latter, as we shall presently see, 
proceed directly to the grey substance. Indeed, I have sometimes felt almost 
persuaded that a great number of the fibres of these posterior roots are directly con- 
tinuous, in the grey substance, with those of the anterior roots ; but I cannot make 
this statement with absolute certainty ; and as the question is one of extreme diffi- 
culty, I shall hereafter endeavour to make it a subject of special attention. 
The second kind of bundles which form the posterior roots b, b, b, Plates XXIII. 
and XXIV. traverse the posterior columns transversely, and with different degrees of 
obliquity from without inwards, extending nearly as far as the posterior median fissure : 
see also Philosophical Transactions, 1851, Plate XXIII. fig. 14. Their component 
filaments are finer than those of the other kind of bundles, measuring, in a recent state, 
about the yoW^h of an inch in diameter. They enter and pass through the posterior 
grey substance at various angles, and in compact bundles which decussate and interlace 
each other in the most complicated manner. Some of their fibres cross over to the 
opposite side, through the posterior commissure, behind the spinal canal; others 
extend into the posterior and lateral white columns ; and the rest may be traced 
deeply into the anterior grey substance, where they separate in various directions, 
and are ultimately lost to view. 
The bundles which compose the third kind of posterior roots enter the chord 
obliquely, c, c, c, Plates I. and II. A few of their fibres proceed near the surface 
both upwards and downwards, and pass out again with the roots above and below 
them. The rest cross the posterior white columns obliquely, and chiefly upwards, a 
small number only passing downwards. Interlacing at the same time with each 
other and the roots already described, they diverge, and for the most part reach the 
grey substance at points successively more distant from their entrance in proportion 
to the obliquity of their course ; the remainder or most divergent taking a longitu- 
