THE LUMBAR ENLARGEMENT OF THE SPINAL CORD. 343 
IL The Course of the Nerve-Rogts. 
The course taken by the nerve-roots, both anterior and posterior, as seen in trans- 
verse sections, has been described with so much exactness by Clarke, that I shall draw 
almost all the details of my description from longitudinal sections, which have been 
less carefully studied. 
The Posterior Roots. — These are attached solely to the posterior columns, of which 
they form by far the greater part; this view is in accordance with Clarke (Philos. 
Trans. 1851), and still maintained in his more recent papers. Stilling, however, 
regards the lateral columns as receiving some fibres directly from the posterior roots ; 
but after careful examination I am convinced that the fibres Stilling figures in this 
situation (which I have had no difficulty at all in seeing very distinctly in preparations 
made by Clarke’s method) do not belong to the posterior roots, which from their direc- 
tion they obviously could not join, but are probably radiating fibres, about to turn 
upwards into the longitudinal columns; this is especially evident in the cord of the 
cat, where the sulcus is quite deep, and the bundles constituting the posterior roots are 
kept very distinct. 
Fig. 8, which is an accurate drawing, made by means of the camera lucida, from a 
longitudinal section across the lumbar enlargement of the calf, will serve to show that 
the course of the posterior roots within the posterior white columns is exceedingly 
intricate. The fibres may, however, be seen to take four principal courses : — 
lst. Fibres which ascend obliquely upwards and inwards, penetrating sooner or later 
into the gray substance, according to the degree of their obliquity. (Fig. 8, b, b.) 
2d. Fibres which may be slightly oblique at starting, but soon assume a directly 
transverse course, sometimes varying this by slightly ascending or descending; these 
fibres are mostly of the finest sort. (Fig. 8, e, e.) 3d. Fibres which enter the poste- 
rior column at various angles, but very soon bend round, often at quite a sharp angle, 
descending in a course more or less oblique. (Fig. 8, c, c.) 4th. Fibres which are 
looped or recurrent, seeming to unite both ascending and descending fibres. (Fig. 8, 
d, d.) Besides these four classes, the first three of which have been already noticed by 
Stilling, every variety of intermediate course will be found, the bundles of fibres being 
braided together in the most complex manner. 
The fibres of the first class, or oblique ascending fibres, seem to be the most numer- 
ous, comprising fully one half of the posterior nerve-roots ; they usually enter the pos- 
terior columns at an angle not far from 45°, pursuing the same course for a consider- 
able distance; after penetrating the outer two thirds of the column, they often vary 
