180 
PROFESSOR A. M. PATERSON ON THE DEVELOPMENT OF 
branch. The splanchnic branch grows gradually in a mesial and ventrnl direction, 
towards the symjiabhetic cord, with which it finally becomes connected. It generally 
divides into two parts, of which one joins, the other passes beyond, the sympathetic 
cord. The fibres which join the cord are traceable into direct continuity with its cells, 
or can be followed forwards or backwards in its substance. The part of the splanchnic 
branch which does not join the sympathetic, can be traced beyond it into the 
splanchnic area. 
This arrangement obtains for the spinal nerves in the posterior thoracic and lumbar 
regions. In the anterior part of the thorax the whole of the splanchnic branch appears 
to be joined to the sympathetic cord. Behind the level of the bifurcation of the aorta 
no splanchnic branches ^^'ere found. In the neck, above the point of origin of the 
vertebral artery, they are unconnected with the sympathetic cord. Instead, they 
proceed from their origin in a ventral and mesial direction external to the vertebral 
artery, and round that vessel, to be distributed to the tissues of the neck lying on 
the dorsal aspect of the sympathetic cord. 
These splanchnic branches correspond to the white Rami communicantes. Tracing 
them back to their origin they are found to be derived from both the dorsal and the 
ventral root of the spinal nerve, of which the latter usually contributes the greater 
number of fibres. 
The gray Rami communicantes appear to arise from the sympathetic cord as cellular 
outgrowths, which find their way along the splanchnic branches towards their central 
connexions. They thus may be regarded as belonging to the group of collateral 
branches from the cord. 
3. The formation of the ganglia on the main cord of the sympathetic is a subsequent 
event, and is subordinate to the connexion of the splanchnic branches of the spinal 
nerves with the cord. The causes leading to the formation of the ganglia are ; mainly, 
the junction of the splanchnic branches, and the accession of a large number of nerve 
fibres at the point of entrance ; the consequent persistence of the cells of the cord, 
which are joined by these nerves, as ganglion cells ; and to a less extent, the 
anatomical relations of the cord to the bony segments, &c., over which it passes, 
which, in their growth, cause indentation of the cord at certain points. 
This view is supported by the condition of aftairs found in dissections of Human 
embryos at various periods of development (3-6 months), where the cord has the 
form of a band or strip, rather than a regularly nodulated chain : and by the evidence 
derived from the normal adult structure, where the “ segmentation ” of the cord 
is apparent, rather than real. 
4. Cephalic termination. The parts derived from the sympathetic cord in the neck 
in front of tlie “ inferior ” cervical ganglion, may be regarded as belonging to 
the peripheral or collateral distribution of the nerve. A fibro-cellular bundle springs 
from the cord and accompanies the vertebral artery; beyond this the original cord, 
which is, at first, limited anteriorly at the level of the mouth, becomes constricted by 
