SYMPATHETIC NERVOUS SYSTEM. 395 



either definitely to determine the antero-posterior limits of the 

 system, or to make certain whether the terminal masses of cells 

 which form the ganglia are connected by a longitudinal com- 

 missure. In a stage slightly younger than L the ganglia are 

 much more definite, the anterior one is situated in the cardiac 

 region close to the end of the intestinal branch of the vagus, and 

 the last of them quite at the posterior end of the abdominal 

 cavity. The anterior ganglia are the largest ; the commissural 

 cord, if developed, is still very indistinct. In stage L the com- 

 missural cord becomes definite, though not very easy to see even 

 in longitudinal sections, and the ganglia become so considerable 

 as not to be easily overlooked. They are represented in PL 13, 

 fig. i, sy. g. and in PL 18, fig. 2, in the normal position immediately 

 above the cardinal veins. The branches connecting them with 

 the trunks of the spinal nerves may still be seen without difficulty. 

 In later stages these branches cannot so easily be made out in 

 sections, but the ganglia themselves continue as fairly conspicuous 

 objects. The segmental arrangement of the ganglia is shewn in 

 PL 1 8, fig. 3, a longitudinal and vertical section of an embryo 

 between stages L and M with the junctions of the sympathetic 

 ganglia and spinal nerves. The ganglia occupy the intervals 

 between the successive segments of the kidneys. 



The sympathetic system only came under my notice at a 

 comparatively late period in my investigations, and the above 

 facts do not in all points clear up its development 1 . My obser- 

 vations seem to point to the sympathetic system arising as an 

 off-shoot from the cerebrospinal system. Intestinal branches 

 would seem to be developed on the main nerve stems of this in 

 the thoracic and abdominal regions, each of these then developes 

 a ganglion, and the ganglia become connected by a longitudinal 

 commissure. On this view a typical spinal nerve has the follow- 

 ing parts : two roots, a dorsal and ventral, the dorsal one 

 ganglionated, and three main branches, (i) a ramus dorsalis, 

 (2) a ramus ventralis, and (3) a ramus intestinalis. This scheme 

 may be advantageously compared with that of a typical cranial 

 nerve according to Gegenbaur. It may be noted that it brings 



1 The formation out of the sympathetic ganglia of the so-called paired suprarenal 

 bodies is dealt with in connection with the vascular system. The original views of 

 Leydig on these bodies are fully borne out by the facts of their development. 



26 2 



