THE SYMPATHETIC NERVOUS SYSTEM IN MAMMALS. 
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the formation of a tibro-cellular commissure, separating off the “ superior ” cervical 
ganglion. This ends anteriorly in a fibrous bundle, which accompanies and is lost 
upon the internal carotid artery, beneath the auditory capsule. The “middle” 
cervical ganglion, when present, is to be regarded as formed of a group of cells which 
have been included in the commissure connecting the superior ganglion with the main 
cord, and which have persisted. The connexions of the sympathetic cord with the 
cranial nerves have not been thoroughly investigated, and reference to them has been 
purposely omitted, as they bear no du*ect relation to the development of the main 
cord. 
The reasons for placing the parts named in the category of peripheral branches are 
that (1) they are essentially out-growths from the main sympathetic cord, and (2) no 
splanchnic branches join them from the spinal nerves. 
5, Caudal termination. The sympathetic cord is at first ill-defined behind the 
region of the kidneys; it gradually extends further back, alongside the aorta and 
middle sacral artery, where the two cords become closely approximated. They become 
gradually more and more attenuated, and finally disappear. Near their termination they 
are joined together on the dorsal aspect of the middle sacral artery by cellular commis¬ 
sures, from which the connecting loop and ganglion impav are developed. No fusion 
of the two cords can be seen until they have reached their permanent posterior limit. 
The sympathetic cord behind the lumbar region may be regarded as belonging to 
the peripheral distribution of the cord for the same reasons as the cervical portion. 
6. The peripheral branches from the sympathetic cord, including the collateral 
ganglia, as well as the medullary portions of the suprarenal bodies, the superior 
cervical ganglia, &c., are formed by out-growths from the cord, which are at first 
cellular. These give rise to ganglia, nerves and plexuses, and are accompanied by the 
parts of the splanchnic branches of the spinal nerves which do not join the ganglia. 
In this category are placed doubtfully the gray Rami communicantes. 
B. The Morphology of the Sympathetic System. 
1. The Secondary Segmentation of the Symgmthetic Cord. 
It has been shown that the main cord of the Mammalian sympathetic is primarily 
unsegmented, that in comparatively old Human embryos the differentiation of ganglia 
and longitudinal commissures is not definite, and that in the adult sympathetic cord 
there is no certain indication of true segmentation, except in the obviously metameric 
splanchnic nerves, which are connected with it. Now, in this respect, the sympathetic 
cord does not differ from, but agrees with, not only the other elements of the nervous 
system, both in vertebrates and invertebrates, but also with all other longitudinally 
placed structures in the body. It agrees, firstly, with the medullary tube, forming 
the cerebro-spinal axis, which, so far as present evidence goes, is formed without any 
sign of segmentation, the spinal nerves being secondary and subordinate formations. 
