MR. 0. S. SHERRINGTON ON OUT-LYING 
3G 
membrane over the lateral column at a point which in the cervical cord lies nearer the 
exit of the ventral than that of the dorsal nerve-root, and in the lumbar and lower 
thoracic cord, is nearer to the dorsal than to the ventral nerve-root. This thickeninof 
occupies a shallow fissure, and is better seen in young animals than in adult. It is 
particularly .evident in the lower thoracic and upper lumbar regions. In fully-growm 
Dogs, in the Monkey, and, to a less extent, in the Human adult, a small septum, more 
marked than any of the neighbouring, projects into the lateral column at the level of 
the ventral extremity of the area of the crossed pyramidal tract; it has repeatedly 
seemed to me that this septum is identical with the thickening of the sub-pial 
membrane found in the still imperfectly developed cord of the young animal. In 
cords in which the crossed pyramidal tract comes to form a large portion of the 
lateral column, it would seem that with the growth of the tract tlie shallow bay 
containing tissue continuous with the sub-pial membrane becomes, so to say, unfolded 
and more shallow, even to disappearance. But a septum thrusting itself into the 
lateral column at the spot records the site of its existence. That the septum is of 
real morphological significance, I believe, from the fact that it divides from one 
another two masses of nerve-fibres, wdiich offer a strong contrast in their appearance. 
On the dorsal aspect of tire septum lie coarse fibres of fairly equable size (cerebellar); 
on the ventral exists an admixture composed largely of fine fibres (ascending antero¬ 
lateral). In the Monkey, in which animal, as I have indicated,* a portion of the 
pyramidal tract lies outside the cerebellar along the surface of the lateral column, 
the fibres of the pyramidal tract, as marked out by the degeneration method, 
generally, when followed along the surface in the ventral direction, cease abruptly at 
the little septum in question. In some instances, especially in the upper cervical 
region, a few scattered fibres belonging to the pyramidal tract may be found on the 
ventral side of the septum; but this appears to be quite exceptional for the cord 
as a whole. But I have never found nerve-cells either in the septum or in the sub-pial 
band. 
Into relation with the deeper region of the lateral column come cells of the lateral 
cornu, especially where that cornu is well developed. The small fusiform cells of the 
lateral horn are for the most part situate in that part of the horn which abuts upon 
the white substance of the column. Cells can very frequently be found not far 
within, but yet distinctly within,! the limits of the wdiite matter surrounding the 
horn, most frequently on the dorsal aspect of the horn. There seems no room for 
doubt that these are out-lying members of the lateral cornu group, A certain 
number of nerve-cells, evidently, I think, also out-lying members of the same group, 
lie further out still separated by a much greater distance from the grey matter. They 
are in every case placed upon fine strands of connective tissue which cross the white 
column (fig. 3, Plate 3), and in these strands are to be found fine medullated nerve- 
* ‘ Journ. of Physiol.,’ vol. 10, p. 429. 
I These are seen in Clarke’s fig. 2, from thoracic cord of Ox, ‘ Phil. Trans.,’ 1869. 
