1895. ] NEW YORK ACADEMY OF SCIENCES. 231 
THE SIGNIFICANCE OF MUSCULAR VARIATIONS, 
ILLUSTRATED BY REVERSIONS OF THE 
ANTI-BRACHIAL FLEXOR GROUP. 
By Geo. S. HUNTINGTON. 
Read by Title, Feb. 11, 195. 
The study of muscular variations, if carried on systematically, 
embracing observations made on a large number of subjects, 
cannot fail to reveal certain finer differentions, which, while lost 
in a mere enumerative record of muscle variations, gain a new 
and important significance when grouped together and com- 
pared in an effort to trace the morphological meaning of the 
variant condition. This becomes most strikingly apparent in 
the case of certain appendicular muscles, and especially of some 
muscles of the fore-limb. The extreme modifications which, in 
vertebrates possessing an anterior extremity, widely different 
functional requirements have impressed on this portion of the 
locomotory apparatus, may properly be held responsible for the 
fact that here variations of the most composite type are to be 
encountered. <A glance at the divergent forms presented by the 
vertebrate pectoral girdle will convince us that the muscular 
structures connected with the same must offer deviations from 
the primitive types, which not only change the arrangement of 
homologous muscles in different forms, but which will afford 
the opportunity for numerous reversions to the original con- 
dition in the case of any individual muscle. 
The specialization of the fore-limb, in exchanging a purely or 
chiefly locomotory function for one which includes or substitutes 
the prehensile function, and the consequent higher development 
of the manus, has more especially served to single out the anti- 
brachial flexor group, and to add to the function of flexing the 
forearm at the elbow-joint the more complicated movements of | 
radial rotation in supination of the hand. In some instances — 
this additional functional requirement has sufficed to specialize 
certain members of the flexor group as supinators, modifying 
the insertion so as to restrict the same chiefly or entirely to the 
radius, and separating a portion of the flexor mass by complete 
cleavage from adjoining muscular strata. 
This is most excellently seen in the so-called Biceps flexor 
cubiti of Man and Primates generally, a muscle which acts as 
