1909-10.] Nervous Mechanism of Alimentary Canal of the Bird. 329 
an offshoot from the cerebro-spinal system, and the various sympathetic 
ganglia and plexuses as outgrowths from the main sympathetic chain. 
Gotte (5), writing in 1872, supported the older theory of Remak, but 
added nothing important as evidence for his conclusion. 
Balfour and Foster (6), in their conjoint paper of 1876, described the 
mesoblastic layer as the origin of nerve tissue, but failed to produce fresh 
evidence in support of their theory. 
In 1877 Balfour (7), in an article on the development of elasmobranch 
fishes, described very minutely short outgrowths from the first portion of 
the spinal nerves. From the position of these outgrowths, and from the 
appearance of small clusters of cells at their terminations, Balfour thought 
it probable that they formed the origin of the sympathetic chain. 
In 1879 Schenk and Birdsall (8) described the results of observations 
made by them on human embryos, and embryonic chicks and rabbits. In 
all three embryos they found the sympathetic chain to originate as masses 
of cells migrating from the spinal ganglia. In one case of a human 
embryo they claimed to have successfully traced outgrowing nerve cells 
from the sympathetic chain to the wall of the intestine. 
Onodi (9) in 1884 published the results of an extensive investigation on 
the development of the sympathetic nervous system in embryonic fish, 
amphibians, reptiles, birds, and mammals. Of these, he found embryonic 
fish to give the most satisfactory results, as the rate of development is 
comparatively slow. 
From a consideration of these results Onodi described the sympathetic 
chain as originating by a process of proliferation and migration of cells 
from the spinal ganglia. The various sympathetic nerve elements in the 
intestinal wall and elsewhere were found to he outgrowths from the 
sympathetic chain. 
In 1890 Paterson (10) made a similar investigation on human em- 
bryos, and embryonic rabbits, rats, and mice. His results may be briefly 
summarised as follows : — 
1. The sympathetic system is developed in mammalia out of cellular 
tissue surrounding the aorta, and is at first quite independent of 
the cerebro-spinal system. 
2. The connection between those two structures is effected by out- 
growths from the spinal nerves. 
3. The various plexuses, ganglia, and non-medullated nerves of the 
general sympathetic system are outgrowths from the sympathetic 
chain. 
In the same year His senior (11) gave a minute description of the 
