450 ME. J. L. CLAEKE ON THE OBEY SEBSTANCE OF THE SPINAL COED. 
cornu: some of them are seen to be continuous mth the cells, especially with those 
which are elongated towards them ; others wind about them in a senes of cniwes, w c , 
like the processes themselves, are frequently dhided in a transverse section*. 
Ill the spinal cord of Man, the form of the grey substance differs in some respects from 
that of Mammalia. Throughout the whole of the dorsal region, the postenor cornua 
stand completely apart, and are joined only at their bases by a narrow transverse com- 
missure Fig. 5, Plate XXL represents a transverse section of the entire gi'ey substance 
about the middle of this region. Each posterior vesicular column (M)_occupies nearly 
the whole inner half of the cervix coinu. It is more or less oval, and, in stmcture an( 
appearance, closely resembles that of Mammalia in the upper parts of the lumbar en ^ge- 
ave HOt accumulated near the centre, but scattered at unequal intervals to the veiy border 
of the cervix, from which some of their processes run out with blood-vessels and fibres 
to the posterior white column. Most of the oval variety are elongated in the direction 
of the cornu, and are continuous by their processes with the transverse commissure, on 
the one hand, and on the other, with the posterior roots of the nerves, which also 
interlace through the mass and sweep round on its outer side. 
Towards the upiier end of the dorsal region the dark oval masses dimmish m size as 
may be seen in fig. 6, Plate XXL They are frequently dinded or broken into smaller 
portions by bundles of the posterior roots in their course to the transverse commissure. 
Lid in connexion with some of their cells. In ascending through the cemcal eiilargc- 
ment they continue to decrease, and at length disappear; but the spaces which they 
occupied along the inner halves of the cornua are still interspersed with a mMtifude ot 
cells and traversed hy the posterior roots, which also sweep ™imd as "suid. <>« t leir 
outer sides, in bundles of considerable thickness (see figs. 8 & 9, Plate XXI.). I le 
cells however, are very much smaller than in the dorsal region; the inajonp- arc 
scarcely larger than those in the middle of the gelatinous substance; but a few ot 
superior size are unequally scattered amongst them. Many are oral, round, and lusi- 
form, especially in the direction of the fibres; others, particularly the larger kind and 
nearer the centre of the cervix, are triangular or irregular m shape, and send out then 
processes on all sides. 
Above the cervical enlargement, the dark masses present nearly the same appear anc 
as m Mammalia ; but they are rather paler, and the cells they contain are of smaller size. 
'I'hc tractus intermedio-Iateram^ also, in Man, closely resenrbles tlmt of Mammaha 
and contains cells of the same kind, but rather smaller (figs, ol & 52, Plate XXIL). 
Tn the upper part of the cervical region, a similar but somewhat larger tract reappears m 
lUe sanL situation, and projects in the same way into the lateral ^ 
T1 XXL F). It increases in ascending to the third parr of nerves (fig. 1.x, Plate ^A. . , 
where the form of the entire grey srrbstance presents a very strrkrng resem airce 
* As tliere are no traces of these groups of cells in the human cord, and I have not found them ui tho 
- a,rhiro-pig, it is probable that they supply the nerves of the fa^J. 
Its large cells are more rrurnerous than in the dorsal regron of Mammaira. 
