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the rabbit, and the rat. It was sometimes absent in the dog and 
frequently absent in the cat (9). 
BisHop HARMAN describes the contribution as present in the 
cat (13). WILFRED HARRIS states that it was absent in his dissections 
of the eat, nor did he find it in the serval or in the lion. He found it 
present in some and absent in others of the cercopithecidae (7). 
SABERTON found it absent in the Chimpanzee (14). 
SHERRINGTON remarks that the nerve-supply to the scalenes, the 
diaphragm, the skin and the cervical sympathetic, all show the brachial 
plexus to be somewhat pre-fixed in man as compared with the ma- 
caque (9). 
My own dissections last year on the apes and on such other mam- 
mals as I was able to procure, confirmed SHERRINGTON’s statement 
and led me to hold the view that the brachial plexus in primates tends 
to be pre-fixed when compared with that of all other mammals. This 
cephalic migration I considered to be an adaptation to the posture 
in order to provide against pressure on the lowest brachial trunk (15). 
Since then I have found that such a view is untenable. In the 
first place, there is no need to invoke cephalic migration of the plexus 
to prevent pressure symptoms. ‘The erect attitude itself involves 
-changes in the position of the first rib of sufficient magnitude to pro- 
vide such against an injury. I have described this compensatory 
action in a more recent paper (16). 
In the second place, the present communication shows clearly 
that in the mammalian series the hinder end of the brachial plexus 
is remarkably constant in its constitution and it is incorrect to state 
that the primate brachial plexus is prefixed. It was because I felt 
the need of a much wider survey of the mammalian plexus that 
I undertook the dissection of the cervico-thoracic nerves which is 
recorded in the present instance. 
I have gathered together the results of my dissections into an 
appendix at the end of the article, and will therefore proceed at once 
to a discussion of their significance. In performing the dissections 
I have attempted as far as possible to ascertain the following :— 
(a) The presence or absence of a communication from the second 
dorsal nerve to the brachial plexus. 
(b) The size of the communication where present, in relation to 
the second dorsal nerve itself. 
(c) The relation of the communication to the sympathetic chain. 
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