232 TRANSACTIONS OF THE [May 13, 
one of the chief radial supinators, while its flexor function is to 
a considerable extent subordinated to this main action. 
In muscles of this type variations are frequently encoun- 
tered, many of them being reversional in character and pointing 
to previous ancestral types of myotecture. 
The definition, which certain muscular attachments obtain by 
specialization of function,is accompanied by the concomitant 
reduction or elimination of other connections which have lost 
their original value and significance in the new sphere of the 
muscle, or would eyen, if retained, interfere with the same. 
The muscle, in returning in an incomplete form to these ob- 
solete conditions, presents reversions to which many of the ob- 
served variations may properly be ascribed. 
No muscle presents these features more strongly developed 
than the Biceps flexor cubiti. The muscle is, next to the Pal- 
maris longus, the most variable in the body, Macalister* in 
his Catalogue of Muscular Anomalies enumerating no less than 
45 separate variations. 
It is our purpose in the present paper to discuss only a cer- 
tain group of these variations, and to endeavor to obtain an in- 
sight into their significance. 
The human material, on which the following observations 
have been made, consists of 464 upper extremities dissected 
during the year 1893 to 1894 in the Anatomical Laboratory of 
Columbia College. 
As the explanation of the probable derivation and significance 
of certain of these variations of the Biceps muscle is closely con- 
nected with the morphology of the remaining antibrachial flexor 
group, it will be desirable to take a general view of the ar- 
rangement of this group, before proceeding to the details. 
In the lowest vertebrates a continuous and non-segmented 
plane of muscular fibres proceeds from the ventral aspect of the 
trunk to the flexor surface of the anterior limb. This condition 
is best represented by the muscular apparatus of the pectoral fin 
in fishes. 
In ascending the scale differentiation leads to the more or less 
complete separation of this muscular mass into layers and strata, 
which may or may not preserve connections with each other, in- 
dicative of their original union. 
A consideration of the general arrangement of the flexors of the 
forearm in higher vertebrates reveals the existence of three main 
divisions or layers,+ more or less blended with each other. 
*Alexander Macalister, Additional Observations on Muscular Anomalies in Human 
Anatomy (ITI. Series), with a Catalogue of the Principal Muscular Variations hitherto 
published. Transact. of the Royal Irish Academy, Vol. XXYV., Pt. I., Dublin, 1872. 
+ G.M. Humphry, Observations in Myology, Cambridge and London, 1872, p. 163. 
