106 BYRNES. [VoL. XIV. 
In his work on the fate of the muscle-plate in the chick, Pater- 
son has been unable to find muscle-buds or structures homolo- 
gous to them taking part in the formation of the limbs. 
According to his interpretation, the limbs are derived wholly 
from the somatopleure. 
Harrison, in a recent contribution to the literature on the 
origin of the fin-muscles in teleosts, has conclusively shown 
that in the salmon neither muscle-buds nor myotome-derivatives 
are essential to the development of fin-muscles. In support of 
this view, Harrison finds that, while most of the fins of the 
salmon follow the rule in deriving their muscles directly from 
the myotomes, in the form of muscle-buds, the median and 
pectoral fins furnish exceptions to the rule. According to 
Harrison, the muscles of the middle portion of the dorsal fin of 
the salmon are developed from muscle-buds, while at the ante- 
rior end of the same fin all of the characteristic structures of 
the fin are developed out of a mass of mesenchyme cells, which 
are entirely independent of the myotomes. In the pectoral fins 
modification has gone still further. The ventral myotome- 
processes arising from the ventral edges of the myotomes in 
the region of the pectoral fins take no part whatever in the 
formation of pectoral fin-muscles, but, after becoming detached 
from the myotomes, unite with one another to form the coraco- 
hyoid muscle. All the characteristic structures of the pectoral 
fins, muscles as well as cartilage and connective tissue, develop 
directly from the somatopleure by the differentiation of mesen- 
chyme-like cells. These two views regarding the origin of 
limb-muscles can no longer be regarded as incompatible when 
both modes of muscle formation occur, not only in different fins 
in the same individual fish, but even side by side in the same 
fin. 
The starting-point in the more recent researches on amphib- 
ian limb-muscles has been the hypothesis that the muscles of 
the limbs are developed from myotome-derivatives which are 
homologous to the muscle-buds in the fins of fishes. According 
to Goette’s! account, the limb-muscles of Bombinator develop 
from cells derived from the outer layer of the muscle-plate. 
1 « Die Entwicklungsgeschichte der Unke,” 1875. 
