1G8 
PROFESSOR A. M. PATERSON ON THE DEVELOPMENT OP 
primary division (/.Z).) is longer and larger, and in the regions of the limbs has 
entered their substance and has divided into dorsal and ventral branches. The 
splanchnic branch (S 2 )l.) can novr be traced to a point midway between the cellular 
sympathetic cord (Sy.) and the origin of the branch from the spinal nerve. It is 
most evident in the thoracic region. In the neighbourhood of the origin of the 
trachea and anterior to that, it could not be found. There the cellular cord was 
very distinct ; the superior primary division and somatic branch were visible, but so 
far as I could discover, no splanchnic branch was present. 
In transverse sections of Rat embryos at about 10 days, hardened in spirit and 
stained with aniline blue-black (Plate 23, fig. 7), the cellular cord of the sympathetic 
(Sy.) has much the same characters as in the last case. It still presents in continuous 
sections a uniform thickness. Cellular outgrowths from it (Br.) can be traced ven- 
trally round the aorta, especially in the region of the kidney, and in front of it, to form 
the collateral ganglia, and to join the suprarenal bodies. Behind that point the cord 
becomes attenuated. The spinal nerve shews an advanced condition of development. 
The superior primary division {S.D.), though well formed, is not yet differentiated into 
its separate roots. The somatic part (So.) of the inferior primary division (I.B.) is 
seen divided into its dorsal and ventral branches (l.2.). The splanchnic part (Spl.) is 
very evident in the region in front of the kidney. Each branch is thick, and directed 
inwards above the cardinal vein (C.V.) ; and reaches almost, but not quite, up to the 
sympathetic cord. The interval between the two varied slightly in different nerves, but 
in no single case was the junction perfectly evident. Round the end of the splanchnic 
branch are large fusiform cells which obscure the ends of the nerve fibres, probably 
mesodermal cells, which are proceeding to form the sheaths of the nerves, possibly cells 
derived from the sympathetic cord and pursuing a central direction. The nerve fibres 
throughout the spinal nerves are larger than before, and appear in the form of wavy 
bands. 
In transverse sections of Mouse embryos at about 11 days (Plate 24, fig. 8), hardened 
in picric acid, and stained with borax-cai mine, development is further advanced. The 
spinal cord is more fibrous ; the anterior commissure is thicker, and the decussation of 
fibres within it more evident. The superior primary division of the spinal nerve (S.D.) 
is now traceable to two independent roots, one dorsal, the other ventral. The splanchnic 
branch (*5ph) has now joined the sympathetic cord (Sy.). The fibres on entering the 
mass present, in transverse sections, cut ends, and cannot be traced into direct com¬ 
munication with the cells. Surrounding the junction of the nerve with the cellular 
cord are groups of cells, some of them in continuity with, and apparently forming part 
of, the sympathetic cord, others resembling the blastema cells surrounding the 
splanchnic branch. Some of the cells of the sympathetic cord are ovoid, or occasionally 
stellate in transverse section, Avith one long process directed towards the nerve, and 
others radiating in different directions, chiefly towards the aorta. These processes 
can be seen joining others from neighbouring cells of the mass, in the midst of "which 
