ME. J. L. CLAEKE ON THE GEET SUBSTANCE OF THE SPINAL COED. 439 
Structure of Caput Cornu Posterioris. 
The caput cornu may be seen even with the naked eye to consist of two different 
portions: 1, an outer and comparatively transparent portion — the gelatinous substance', 
2, an inner and more opake portion, or base. 
1. The outer portion or gelatinous substance consists of — 
A. Nerve-fibres. 
B. Nerve-cells. 
C. Blood-vessels. 
D. Connective tissue with nuclei. 
A. The nerve-fibres are transverse, longitudinal, and oblique. — The transverse fibres, 
proceeding from different parts of the grey substance, run backwards across the gela- 
tinous substance in a kind of radiating series of bundles, and in planes at right angles 
to the axis of the cord (fig. 1, Plate XIX.). The bundles near the middle line (as seen in a 
transverse section) are straighter and more parallel than the rest, but partly join or cross 
each other near the posterior border of the gelatinous substance, from which they run 
out through the posterior columns as radiating fibres and posterior roots of the nerves. 
The bundles on each side take a curved direction towards the middle line, but before 
they pass out, their fibres describe a series of arcs of different lengths within the margin 
of the gelatinous substance : along the inner side of the latter there is always a large 
bundle which subdivides and runs out towards the posterior median fissure ; and from 
the outer side of the gelatinous substance a smaller number of fibres proceed through 
the posterior part of the lateral column. The primitive fibres composing these bundles, 
as I showed on a former occasion, are not grey fibres, but tubules of small average size, 
the larger kind possessing double contours. By far the greater number vary from about 
the to the rorWofh of an inch in breadth, but are intermixed with others of 
about the of inch in diameter. The marginal fibres within the posterior 
border of the gelatinous substance are more often of the latter kind. 
The longitudinal fibres of the gelatinous substance are very numerous, and resemble 
the finer tubules of the transverse bundles*. 
The oblique fibres, which are found in different planes, are in various degrees inter- 
mediate in direction between the two former sets, and, as I formerly stated, are appa- 
rently continuous on the one hand with the longitudinal, and on the other with some 
of the fibres of the posterior rootsf. 
* These fibres were more fully described in my first communication, Philosophical Transactions, 1851, 
Part II. p. 610. 
t In his first treatise on the Spinal Cord, Stilling described all the fibres of the grey substance as grey 
fibres, but in his recent work they are shown to be tubules. He seems to think that I was not acquainted 
with the fibres which take an oblique course through the gelatinous substance. It is true that I gave no 
separate description of them, but in the explanation of fig. 2, Plate XX., Philosophical Transactions, 1851, 
Part II., when speaking of the bundles which project into the substantia gelatinosa from the grey substance, 
I observed that “ this appearance is caused by oblique sections of bundles of nerves and blood-vessels which 
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