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Proceedings of the Royal Society of Edinburgh. [Sess. 
pre-aortic plexus, chains of cells passed down the mesentery to the gut 
wall (PL II. fig. 3, PI. IY. fig. 2). These mesenteric nerve chains showed 
a marked increase in development from the sixth day, besides a 
sharper definition with the silver stain. In the gut wall, both in stomach 
and intestine, the two layers of nerve cells were clearly seen (PI. IV. 
fig. 3). The outermost layer, which was directly connected with chains of 
sympathetic cells in the mesentery, still showed the cells arranged in small 
clusters situated somewhat apart and connected by delicate nerve fibres. 
In the deeper layer the cells are arranged almost singly, but closely inter- 
woven by their outgrowths. The vagus fibres were widely spread over 
Fig. 3. — -A, liver ; B, vagus fibres in wall of stomach. 
the stomach wall (line drawing), a few extending to the first portion of the 
small intestine. These fibres form a fine interlacing network, and mix 
freely with the more lightly stained fibres belonging to the sympathetic. 
Nowhere was any actual connection found between the vagus fibres and 
the cells lying in either layer in the gut wall. In the lower intestine the 
plexiform nerve layer described at the sixth day was found better 
developed, while a few nerve cells were seen at the outer margin. The 
cylindrical band of nerve cells and fibres forming the intestinal nerve of 
Remak already referred to was found definitely connected with the lower 
portion of the sympathetic (PI. II. fig. 4, PI. IV. fig. 4). The outgrowths 
from the lower portion of the spinal cord, noted at earlier stages 
as extending to the pelvic plexus, were better developed, and from their 
position seemed to correspond to the nervi erigentes. 
The chick embryo therefore showed at this age a complete chain of 
nerve cells and fibres from the spinal cord, via the rami communicantes 
