THE SYMPATHETIC NERVOUS SYSTEM IN MAMMALS. 
163 
and rami are dmect proliferations from the spinal ganglia. Nor in either case is the 
evidence clear regarding the fusion of the ganglia to form the connected chain. 
In Birds and Mammals, Onodi did not see tlie earliest stages in tlie development 
of the sympathetic. In the Chick at 3 and 5 days the gangliated cord was 
present, and connected by rami to the spinal nerves. In the Rabbit (10 mm.) and 
Human embryos (18 mm.) the same conditions were found—ganglia already formed, 
with their rami communicantes. These observations do not differ markedly from those 
of other investigators—His, Schenck and Bildsell, Braun, &c. Yet, although in 
no case were the ganglia seen to spring from the spinal ganglia, Onodi expresses him¬ 
self as convinced (from the appearance he describes in Scyllium) that that is the source 
from which they originally start. 
Summarising the conclusions of previous observers discussed above,—the sympa¬ 
thetic gangliated cord in Mammals consists of vasomotor ganglia, trophic in their 
functions, and pseudo-metameric in their morphological arrangement. Two opposite 
views exist amongst embryologists regarding its development. In both views the 
segmental formation of the cord is upheld. According to one view it is mesodermal, 
and is formed in situ. Accordino’ to the other view, it is ectodermal. But the 
observers who assert this view disagree as to its fundamental source. Balfour 
regards each ganglion as an offshoot from the spinal nerve ; Onodi and Schenck and 
Birdsell consider it as a direct proliferation from the spinal ganglion. 
In the succeeding pages the attempt will be made to find the source of the sympa¬ 
thetic system in Mammals, by tracing its development from its first appearance to the 
date at which it can be fairly compared with the adult condition; and thereafter, by 
a study of its morplrology at different ages, and in different animals, to harmonise the 
conflicting views of anatomists and physiologists, 
II. The Development of the Sympathetic System."' 
The following researches were begun some years ago, during an investigation into 
the development of the spinal nervous system. It was then noted that the first 
apparent connexion between the sympathetic ganglia and the spinal nerves arose in 
the formation of the splanchnic or visceral branch of the latter, which passed into the 
splanchnic area and seemed to join the gangliated cord. Beginning at this point, and 
continuing the investigation into earlier and later stages, it has been possible to 
arrive at conclusions reo-ardirm the main features in the formation of the gangliated 
* Dealing exclusively with Mammals, in the following pages, it is necessary to explain the method 
used in determining the ages of the embi’yos employed. It is not possible, in my opinion, to be certain 
as to exact ages, as the time of impi’egnation after connexion varies in different cases ; and two embryos 
from the same uterus often differ in size and extent of development. From a comparison of a large 
series, however, it is possible to determine approximately the age of a gNen embryo. In the following 
description the probable age of the embryo is given, and when possible, its axial length also, 
Y 2 
