334 THE LUMBAR ENLARGEMENT OF THE SPINAL CORD. 
oblique plane, run fully into the cornu lower down. I have never met with true nerve- 
cells (cells giving off distinct nerve-tubes) in any other situation in the white substance. 
My own observations are entirely in agreement with the description which J. L. 
Clarke* has given of the connective tissue. I have, however, frequently noticed in the 
cords of adult animals that a few of the cells were still persistent, especially in the 
vicinity of the posterior cornua, where I have several times seen quite large cells send- ` 
ing out fine processes continuous with the connective tissue. The view which Clarke 
has taken of the possible relation between connective and true nerve-tissue seems very 
valuable; for I have long been satisfied of the impossibility of fully distinguishing, 
with our present means, between these two tissues, which seem to run into each other 
so closely as to suggest very strongly the important question, * whether there is any 
actual and essential difference between them, or whether the connective tissue of the 
cord be intermediate in its nature, passing on the one hand into nerve tissue, and on 
the other into pia mater.” f Every observer who has in his possession moderately 
transparent specimens must be able to satisfy himself of the entire incompleteness of 
the views of Bidder and others, in whose opinion the greater part of the gray sub- 
stance consists of connective tissue. 
The gray substance is composed of nerve-cells, connective tissue, and nerve-fibres 
running in various directions, transverse, oblique, and longitudinal. 
The form of the gray substance has been so fully and faithfully described and 
figured by Clarke t and Stilling,§ that I shall proceed at once to consider: — 
I. The Nerve-Cells, their Situation, and the Relation which Cells and Fibres bear to 
each other. 
(A.) The Nerve-Cells. — The form of these has been fully figured and described by 
Clarke, Kólliker, R. Wagner, Stilling, and many others. The cells are subject to great 
variation, the apparent form, size, and number of processes depending, without doubt, 
very much on the direction of the plane of section with respect to the situation of the 
cell. With regard to the distinctions which Jacubowitsch|| has founded on the size of 
the cells, dividing them into motor, sensitive, and sympathetic, according to their rela- 
tive dimensions, I fully agree with Stilling as to the absolute impossibility of making 
any such classification in our present state of knowledge, and a glance at any of the 
* Philos. Trans., 1859, Pt. I. p. 441. T Ibid., p. 442. 
i Philos. Trans., 1851, 1853, 1859. 
$ Neue Untersuchungen über d. Bau d. Rückenmarks. Cassel, 1850 — 59. 
| Bulletin de l'Académie de St. Petersburg. 1856. 
