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sympathetic chain seemed to call for further investigation of its con- 
stitution. 
PURVES STEWART indicates that the second dorsal nerve contri- 
butes some of the cutaneous fibres to the post-axtal border of the 
upper arm (4). 
HEAD gives it the same share in the cutaneous supply of the arm(6). 
THORBURN, ou the other hand, does not mention it as contri- 
buting any cutaneous fibres (5). 
Harris states that the second dorsal nerve contributes motor 
fibres to the muscles of the hand (7). 
In such cases the fibres would probably reach the thenar muscles 
through the communication between the ulnar and median nerves 
in the fore-arm, which occurs in 20 to 25% of cases in man (8). 
SHERRINGTON describes a variety of communication between 
the first and second dorsal nerves in which the branch passes back- 
wards from the first to the second nerve. He also states that in some 
cases the second dorsal nerve supplies fibres to the muscles of the hand 
and to the skin of the upper arm, but not to the skin of either the 
fore-arm or the second intercostal space (9). 
In animals also there is considerable variety in the views expressed 
regarding this contribution. 
SHERRINGTON describes it as occurring constantly in the macaque 
and states that it supplies fibres to all the muscles of the hand and the 
flexors of the wrist. Stimulation of it produces flexion of the thumb 
and fingers, and sometimes also supination and pronation. 
The variety in which the communication is backward from the 
first to the second dorsal does not occur in macaques, according to 
SHERRINGTON (9). 
FERRIER and YEO state that the second dorsal nerve supplies 
the interossei in the macaques (10). 
In these animals also the muscular fibres reach the muscles of 
thenar eminence through the communication between the ulnar and 
median nerves in the fore-arm. HEPBURN describes this communi- 
cation as normal in most apes (11), though SHERRINGTON states that 
it is not present in cercocebus, nor in cynocephalus (9). BARDELEBEN 
describes this communication between the ulnar and median nerves 
as being present in most mammals (12). 
SHERRINGTON states that he found a contribution from the 2nd 
dorsal nerve to the brachial plexus in monkeys, and in the horse, 
O* 
