674 : THE NERVOUS SYSTEM. 
Another account of the development of the sympathetic system, supported by high 
authority, describes the gangliated cord as an outgrowth of the dorsal ganglia of the 
spinal nerves. It is said that each ganglion gives off a bud at its lower end, which, grow- 
ing inwards into the splanchnic 
area, becomes attached to the trunk 
of the spinal nerve just beyond the 
union of the dorsal and ventral 
roots. The bud still extending 
inwards into the splanchnic area, 
remains associated with the nerve 
by an attenuated stalk. These buds 
become the ganglia, which, after 
reaching their permanent place in 
the splanchnic area, are supposed 
to extend upwards and downwards 
so as to coalesce and form a beaded 
chain of ganglia. The stalks con- 
necting the ganglia with the spinal 
nerves become the white rami com- 
municantes. This mode of develop- 
ment does not satisfactorily account 
for several important features of 
the sympathetic system—the de- 
velopment of those parts of the 
Fic. 483.—SrctioN THROUGH THE SYMPATHETIC GancriaTep angliated cord which possess no 
CorD OF AN EMBRYO. white rami, the absence of a real 
Showing the connexion with the ganglion (Sy) of the white segmental character in the cord 
ramus communicans (Spl); (a) a portion of the ramus join- (remarkably shown in the foetus), 
ing the ganglion ; (8) fibres passing over the cord, accom- and the constancy of continuity in 
panied by a stream of cells; (y) continuous with those of ae Sys F a 
ie cane lian (ia eee the gangliated cord. No instance 
is recorded of a hiatus between 
two ganglia. It is a tempting view on the other hand, as it ascribes to the one germinal 
layer (epiblast) the formation of all the elements of the nervous system, and it brings the 
sympathetic ganglia into serial homology with isolated ganglia on the cranial nerves (eg. 
the ciliary, spheno-palatine, and otic, on the trigeminal nerve). 
The Morphology of the Sympathetic System. 
From a consideration of its structure, functions, and development, there appear to be two 
separate structures represented in the sympathetic nervous system—the spinal and the sym- 
pathetic elements. The structure of the system presents a union of two distinct elements—fibres 
of cerebro-spinal nerves and “sympathetic” cells and fibres. While the function of the 
gangliated cord and its branches seems to be absolutely dependent upon the cerebro-spinal nervous 
system, it is certain that the cells and fibres of the sympathetic system possess a vital activity 
apart from their connexion with the central nervous system. In the development of the 
sympathetic it is at least highly probable that a mesoblastic rudiment or precursor forms the 
basis of the sympathetic system, which is secondarily joined by nerve fibres from the roots of the 
spinal nerves. 
Morphologically this part of the nervous system is essentially a longitudinal cord or column, 
associated with involuntary muscles and glandular tissues, and particularly related to the organs 
in the splanchnic area. Like other longitudinal structures in the body, and especially like the 
organs of the splanchnic area, the sympathetic system is not truly segmental. The gangliated 
cord is only quasi-segmental, the segmentation being attributable to its junction with the 
visceral branches of the spinal nerves. The peripheral branches from the gangliated cord are 
not segmental ; even the gray rami are not properly metameric, but, like the ganglia, assume a 
segmental character in consequence of their connexions with the spinal nerves. 
The phylogenetic relation of the sympathetic and the cerebro-spinal elements in the system 
it is impossible to determine. It may be that the sympathetic system is the representative of 
an ancient architecture independent of the cerebro-spinal nervous system, the materials of which 
are utilised for a more modern nervous system; or it may be that the correlation of spinal 
nerves and sympathetic are both the consequences of the formation of new organs and structures 
in the splanchnic area. Examined in every light, it possesses features which effectually differ- 
entiate 1t from the cerebro-spinal system, although it has become inextricably united with it 
and subservient to it. 
