SYMPATHETIC! SYSTEM 135 



ganglia as formed from outgrowths of the spinal nerve-roots (Balfour), the 

 cells of the outgrowths being identical with those which give origin to the nerve- 

 trunks, and becoming differentiated 'in situ into ganglion-cells. Another 

 account regards the sympathetic simply as detached parts of the spina 

 ganglia, the errant ganglia thus produced remaining attached to the spinal nerve 

 by the ramus communicans, and becoming secondarily connected together to form 

 the gangliated chain. His showed that in the human embryo the visceral branches 

 of the spinal nerves appear before the ganglia. He accordingly modified the 

 interpretation in the sense that the elements which form the sympathetic ganglia 

 are not formed nerve-cells, but indifferent cells which, arising in the spinal ganglia, 

 wander passively or actively along the previously formed nerve-paths to become 

 aggregated into groups or primitive ganglia, where their transformation into 

 nerve-cells is completed. A third interpretation goes one step further, and 

 describes the growth of the sympathetic as a part merely of a general extension 

 in the developing nerve-paths of indifferent ectoderm cells, which undergo their 

 differentiation into nerve-cells, sheath-cells, or chromophil- cells only when they 

 reach their peripheral situation (Kohn [ ) (see p. 100). 



None of these interpretations of the appearances seen are easily capable of 

 objective proof, but the weight of evidence is decidedly in favour of the purely 

 ectodermic origin of the sympathetic, and of the discrete spread of indifferent 

 cells. 



The sympathetic first appears in the form of groups of cells closely applied to 

 the ventral branches of the spinal nerves. Each of these soon becomes a cellular 

 cord which is the rudiment of the ramus communicans. The ramus communicans 

 next becomes fibrillar, and the ganglion is produced by proliferation of a 

 terminal group of cells (fig. 170). The primitive ganglia are secondarily connected 

 by cellular strands into a continuous cord, which becomes segmented later by the 

 conversion of the intervening strands into nerve-fibres. There is little doubt that 

 the whole system of plexuses and ganglia is formed by extension due either to 

 proliferation or to wandering of the cells from the primary chain. In the neck 

 the cord is closely related to the vagus, and the branches of the two are bound up 

 in a common plexus for the supply of the heart and lungs. The superior 

 cervical ganglion is said to be derived from the ganglion nodosum of the vagus, 

 and perhaps also the ganglion of the glossopharyngeal (His, Jr.). The abdominal 

 sympathetic consists at quite early stages of many groups of cells round the 

 aorta, and many scattered groups which extend into the mesentery, through which 

 the cells reach the stomach and intestine. The cells form a single layer in the wall 

 of the stomach, afterwards separated into the two plexuses by the formation of 

 the muscular coats (His, Jr.). 



Chromophil, chromaffin, or phdochrome bodies. It has within recent years been shown 

 that, more especially in the region of the abdominal sympathetic, but also along the whole 

 extent of the sympathetic cord, groups of cells are formed from the primary indifferent 

 sympathetic cells, which have the special property of staining yellow brown with the 

 salts of chromic acid. This chromophil system is represented in the adult by the medulla 

 of the suprarenal body, and perhaps also by the carotid and coccygeal glands. Such chromophi 

 bodies, first discovered in the human embryo in 1901 by Zuckerkandl, are seen grouped 

 more especially between the kidneys and suprarenal bodies, extending downwards along the 

 ureters into the pelvis. They consist of groups of large clear cells with very lightly staining 

 nuclei (fig. 257, p. 204), and contrast strongly with the groups of densely arranged smaller and 

 deeply staining cells traversed by nerve-fibres which are the rudiments of the sympathetic ganglia. 

 It is more especially to the researches of Kohn that the recognition of the system in the human 

 subject is due. It appears certain that the cells are sympathetic in origin ; they occur not only 

 in masses, but in scattered groups in the ganglia. The histogenesis is conceived briefly 



1 Kohn, Arch. f. mikr. Anat. Ixx. 1907. 



