170 
PROFESSOR A. M. PATERSON ON THE DEVELOPMENT OF 
In Rat embryos, at about 13 days, hardened in spirit, and stained with aniline 
blue-black, the sympathetic cord can be followed backwards as far as the middle 
sacral artery, and slightly behind the bifurcation of the aorta. In coronal sections in 
the thoracic region, it shows no constriction whatever ; it is composed of fusiform cells 
arranged longitudinally, with nerve fibres coursing forwards and backwards among 
them, derived from the splanchnic branches of the spinal nerves, which can be seen to 
enter the cord obliquely, the fibres diverging and being traceable for some distance. 
The cellular branches from the sympathetic cord have now extended stiU further in a 
ventral direction, and the formation of the collateral ganglia and suprarenal bodies is 
more advanced. The splanchnic branches first become evident and join the sympa- 
tlmtic cord at the point where the dorsal aorta becomes single and median. In front 
of that point there was no evidence of a splanchnic branch joining the sympathetic 
cord. Again, behind the bifurcation of the aorta no splanchnic branches could be found. 
Between these points they were distinct and evident. In the region of the stomach 
and kidney the splanchnic branch was most clearly divisible into two parts, one join¬ 
ing the sympathetic, and the other passing round the outer side of it accompanied 
by a cellular branch from the cord, to join the semi-lunar ganglia, or solar plexus. 
In Rat embryos about 14 days, stained with borax-carmine or aniline blue-black, 
the mesoderm has begun to show signs of cartilage formation. At this date the 
sympathetic cord still presents no sign of constriction, except at the anterior end. 
At the point of origin of the vertebral artery—the point to which it could originally 
be traced—it becomes narrow, its tenuity being due to the presence of nerve-fibres, 
and largely to the absence of cells. Having given off a large fibro-cellular cord, which 
accompanies the vertebral artery, it again swells out to form the “ superior” cervical 
ganglion. This lies close to the ganglion of the vagus, with which it appears to com¬ 
municate. It can be traced, as before, along the internal carotid artery to the auditory 
capsule, beneath which it becomes first fibrous, and then, gradually attenuating, finally 
disappears. The vertebral artery at its origin is completely surrounded by the 
cellular cord. There is no change at the caudal end. 
The splanchnic branches in the thoracic and lumbar regions can now be traced 
proxirnally to the roots of the spinal nerves, and are found to receive fibres from both, 
especially the ventral roots. In the neck, in front of the origin of the vertebral 
artery, there is no sign of splanchnic branches joining the sympathetic. Branches, 
however, are seen springing from the ventral roots of the cervical nerves, which course 
horizontally inwards round the under surface of the vertebral artery, and become lost 
in the piotovertebral mass around the notochord. These branches are situated at 
some distance from the sympathetic, on its dorsal aspect. As they are traced back¬ 
wards successively towards the origin of the vertebral artery, they approach nearer to 
the cord, and finally, behind the origin of the vessel, the splanchnic branches proper 
appear, and partly join, partly pass over, the cord. 
This latter arrangement is most obvious, however, in the posterioi- dorsal and 
