174 
PROFESSOR A. M. PATERSON ON THE DEVELOPMENT OF 
of the presence of tlie sympathetic cord is found in isolated, segmentally-arranged 
masses, whicli in successive sagittal sections grow larger and larger, gradually fuse 
together, and give rise to a continuous fibro-cellular cord. The condition of the 
cord {St/.), cut through in its thickest part, is indicated in fig. 12. It is mainly cellu¬ 
lar, uniform in width except at certain points, and with a considerable admixture 
of nerve fibres on its ventral aspect. It is joined, dorsally, in the intervals between 
the vertebras, by the splanchnic branches of the spinal nerves (Spl.), and at these 
“ nodes” the cord has a greater width than in the intervals between them. 
In this condition is seen the first commencement of gangliation or nodulation of 
the sympathetic cord. Two causes produce it : (1) the union of the splanchnic 
branches. This causes the cord at a given spot to attain a larger size, by the acces¬ 
sion of a bundle of nerve fibres, some of which join the cells of the cord, and so insure 
their permanent occupation of that S})ot, as the cells of the ganglia ; and (2) the 
position of the cord in relation to the vertebral column. By the growth of the latter 
the cord is stretched, and the part lying against the vertebral somites is elongated 
and narrowed, and is indented by the growing vertebrse and intercostal vessels, the 
result being the formation of a longitudinal fibro-cellular commissure connecting the 
nodes or ganglia together. The ganglia themselves are permitted to increase in size, 
by their position, and by their connexion with the splanchnic branches of the spina 
nerves. The commissures, at first cellular, become fibro-cellular, and afterwards 
fibrous, owing to the admixture of spinal fibres, and apparently also to the con¬ 
version into fibres of the original cells of the cord. By the formation and gi'adual 
constriction of the commissures the ganglia are made still more definite. 
This process of ganglion formation, due primarily to these two causes, can be followed 
in older embryos ; but as the parts gradually attain their adult form the regularity of 
alternate swelling and constriction is not so evident. As the ganglia become defined 
in form, their position tends to become irregular. While one may lie in the interval 
between two vertebrm, the next may be seen opposite the vertebra itself. Again, two 
ganglia may be co-terminous, not by fusion, but from the fact that separation is 
incomplete. Tl)is arrangement is shown in Plate 29, fig. 18, taken from a sagittal 
section of a Bat embryo at about 22 days. The sympathetic cord {Sy.) is figured in 
the region of the diaphragm {Di.), just beyond the point at wliich the stream of cells 
arises for the formation of the semilunar ganglion {S.G.) and solar plexus {Sol.). The 
cord is constricted at intervals, so as to form ganglia and commissures, both of which 
are irregular, and bear, as may be seen, no definite relation to the vertebral 
segments (P.'S'.) or intercostal vessels {Tnt.). The commissures are, for the most 
part, fibro-cellular ; in some instances they are maiidy fibrous ; in others there are 
groups of cells enclosed among the fibres : wliile in others again there are compara¬ 
tively few fibres, so that the ganglia ai'e practically fused together. The cord is here 
represented in its greatest thickness ; in sections on either side the irregularity of 
the ganglia (into which splanchnic brauches can be traced) is much more marked. 
