178- 
PROFESSOR A. M. PATERSON ON THE DEVELOPMENT OP 
p. 166), beliind the point at which the mass of cells arises for the formation of the 
suprarenal body, the cord is irregular in form, and composed of cells less closely 
packed together than in anterior regions. At a slightly later period it has extended 
further backwards (Rat, 12 days, Plate 27, fig. 14a), and becoming attenuated is 
lost at the point of bifurcation of the aorta. In still older embryos it passes further 
backwards on each side of the middle sacral artery, and on the dorsal aspect of the 
rectum, from which it is separated by cellular tissue. 
In Rat embryos of 22 days the cord {Sy., Plate 30, fig. 20) can be traced backwards 
in successive transverse sections for a considerable distance, lying in the interval 
between the middle sacral artery [m.s.) and its accompanying veins (v.v.). The cords 
of the two sides approach one another as they pass backwards. Cellular branches (Br.) 
arise from them at intervals, and are dii’ected downwards between the vessels. The 
cords themselves are more irregular in form than anteriorly, and are not joined by 
splanchnic branches. Near their ])osterior terminations, having approached very close 
to one another, they become connected here and there by transverse cellular com¬ 
missures (Co.) of which one is represented in fig. 20. These are not in direct con¬ 
tinuity with one another, but are separated by intervals, and beyond them the two 
cords taper oflP, and finally are lost in the undifferentiated mesoblast above the middle 
sacral artery. These commissures, which lie close together, and are formed by the 
fusion of outgrowths from the two cords, apj^arently give rise to the 6bres con¬ 
necting the adult coccygeal ganglia together, which form the loop containing the 
coccygeal ganglion, or ganglion impar. It is only in an advanced condition of 
development that the fusion of the two cords can be made out ; until they have 
reached their ultimate limits the fusion does not take place. 
The posterior, like the anterior end of the sympathetic cord, may be regarded as an 
outgrowth from the original cord. It is formed by an extension of the cord back¬ 
wards along the main vascular trunks, and it likewise receives no splanchnic branches 
from the spinal nerves, 
5. Collateral Distribution. 
{a.) The development of the superior cervical ganglia,, the carotid and vertebral 
plexuses, has already been traced, and the opinion has been expressed that these 
structures properly belong to the collateral distribution of the sympathetic cord. 
(6.) Regarding the formation of the peripheral branches, and collateral ganglia of 
the sympathetic, my investigations in the main support the conclusions arrived at by 
Remak (5, 6). As already noted, cellular buds or branches arise from the sympa¬ 
thetic cord (figs. 7 and 13, Plates 23 and 26), and accompany the parts of the 
splanchnic branches of the spinal nerves which pass beyond it. These cellular out¬ 
growths gradually increase in length and thickness. They consist of cells which 
resemble in every way those of the sympathetic cord itself They communicate by 
