J. Playfair MceMurrich 189 
thirds of the radius and ulna, its upper border occasionally, however, 
reaching almost the proximal ends of the bones. 
If, now, we attempt to employ the nerve supply of these muscles as 
a guide to their homologies in the lower vertebrates, we are at once 
met with the difficulty that the arrangement of the nerves in the 
mammalia is very different from what was characteristic for the lower 
forms. In place of the single nervus brachialis inferior longus enter- 
ing the forearm to supply all its flexor muscles, there are two such 
nerves, the ulnar and the median. In a general way the ulnar corre- 
sponds to the R. superficialis ulnaris of the lower forms and the median 
to both the R. Profundus and the R. superficialis radialis, but the homol- 
ogy cannot be carried into detail. Indeed, from what I have observed 
in the forms I have studied, I am inclined to believe that the median 
and ulnar nerves are not perfectly equivalent throughout the mam- 
malian series, the ulnar, for instance, in one case containing fibres 
which in another case are included in the median. That such may be 
the case has already been pointed out by von Bardeleben (1891), who 
finds in the mammalia a plexus formation between the median and 
ulnar in the proximal part of the forearm, and Kohlbrugge (1897),° 
arguing from the differences he finds in the nerve-supply of apparently 
homologous forearm muscles in different mammals, goes so far as to 
maintain that the median and ulnar nerves are not to be regarded as 
definite and invariably equivalent nerves, but merely as paths which 
may conduct elements of different origins. 
I may say that in the arm of the human embryo I employed in the 
present study, a strong branch was given off from the median at the 
level of the branching of the brachial artery and, following the course 
of the ulnar artery, it passed obliquely inward between the sublimis 
and profundus muscles to join and become completely incorporated in 
the ulnar nerve. Krause and Telgmann (1868) mentioned this con- 
dition as of occasional occurrence in man and state that it is almost 
constant in apes. 
But while we cannot employ the nerve supply as a certain basis for 
the homologies of the mammalian muscles, yet it may yield accessory 
evidence if we can determine the general plan of the rearrangement of 
the nerve fibres, which has taken place. I believe the rearrangement 
may be pictured as being along the following lines: 
2T regret that I have not been able to consult this paper. The statement made 
concerning it is based on the review of the paper by von Bardeleben in the Ergebnisse 
fiir Anatomie und Entwicklungsgeschichte, Bd. IX, 1899. 
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