OF MYRIAPODA AND MACROUROUS ARACHNIDA. 
299 
as I formerly had the honour of stating to the Royal Society. Both these series 
may be traced along the whole cord upwards to the cerebral ganglia, and hence may 
fairly be inferred to minister to volition and sensation, either separately, or, as there 
seems reason to believe, conjointly, through a mutual, partial interchange of fibres ; 
although it appears almost impossible to demonstrate, with certainty, by any experi- 
ment on these structures, the precise individual function of either series. The infe- 
rior series is swelled out in each half of the cord, in every segment, into ganglia, 
from which nervous trunks are given off ; while the superior series passes longitudi- 
nally over the ganglia, without becoming perceptibly enlarged, or entering into the 
composition of these ganglia. These enlargements of the cord are produced, in part, 
by a slight enlargement of the longitudinal fibres themselves, and in part also by the 
interposition between them of nucleated cells, which are chiefly collected in the middle 
portion of each ganglion. The ganglia are traversed transversely by fasciculi of com- 
missural fibres, which form part of each nerve given off from the ganglia, as shown by 
Dr. Carpenter, myself, and others. Those fasciculi of fibres which pass through 
the ganglia are equal in number to the nerves given off from them, and enter into cor- 
responding nerves on either side. They form no direct connexion with the brain, nor 
with any nerves anterior or posterior to them in the cord, but only with the corre- 
sponding nerves on the opposite side of the ganglia. Their function may therefore 
be regarded as commissural and reflex ; combining in action the two opposite sides 
of that segment of the body to which they are distributed. But there are other fibres 
that form part of the sides of the cord which combine distant parts and segments on 
the same side, and which, although extending longitudinally in the cord, in part of 
their course, have no direct connexion with the brain, nor are traceable to that organ. 
Hence the function of these also, which have not before been pointed out by anato- 
mists, must be regarded as reflex, and as combining distant organs or segments on 
the same side of the body, as the commissural fibres do parts on the opposite side in 
the same segment. These fibres form the exterior of the nerves and cord. Tracing 
them from their peripheral extremities, on the surface of the body, they pass inwards 
to the spinal cord in the course of the nerves, bounding the posterior surface of the 
root of each as it comes from the ganglion. They are then reflected backwards, 
and form the postero-lateral surface of the cord, into the composition of which they 
enter, and along which they are extended backwards until they arrive at the ganglion. 
They then again pass outwards on the ganglion, forming its antero-lateral surface, to 
the root of a nerve, along the anterior of which they pass to their peripheral distribu- 
tion on the surface of the body. Some of these fibres, after joining the cord, seem 
to pass beyond the next ganglion to be given to nerves from one more distant, so 
as to form, as it were, a series of circles one within the other. These fibres are 
joined with all the nerves of the body, both those which pass directly from the gan- 
glia, and those which seem to come from the upper or aganglionic portion of the 
cord. Now since these fibres have no direct communication with the brain, as may 
MDCCCXLI1I. 2 R 
