J. Playfair MeMurrich 495 
The second suggestion would therefore seem to be the more satisfac- 
tory one; but, again, there are diificulties in the way of its being regarded 
as altogether sufficient. It is true that we find double lumbricales or a 
double insertion for them in the marsupials and monotremes, and it 
might be supposed that there is fundamentally a similar condition in 
man, sometimes persisting to the adult condition, but more usually giv- 
ing place to a single insertion. The finding of a double insertion of 
the third lumbrical in an embryo of 4.5 em. and but a single insertion 
in an embryo of 6 em. is suggestive, but it completely loses weight when it 
is noted that in the younger embryos studied by Lewis (1902) this lum- 
brical had but one insertion. Furthermore, it is noticeable that while in 
the lower mammals it is the second and third lumbricals which are 
doubled, the second muscle in man is remarkably constant in possessing 
but one part, and, furthermore, a double insertion occasionally occurs 
in the fourth muscle in man, Kopsch and Reinhardt each recording ten 
cases of this nature, while Kopsch records four cases and Reinhardt one 
of a single insertion of the muscle into the ulnar side of the fifth digit.’ 
It would seem, then, that neither of von Bardeleben’s suggestions sat- 
isfy the requirements of the case, nor does there seem to be any morpho- 
logical explanation of the variation at present available. May it not be, 
after all, that there is no such explanation required, what is required 
being rather a physiological explanation ? 
For, as has been seen in comparing the muscles of the amphibia, rep- 
tilia and mammalia, the shifting of an msertion from one digit to the 
adjacent side of another is by no means an uncommon phenomenon. In 
other words, there is not that morphological isolation of the digits from 
one another which we are apt to imagine; the hand develops as a whole 
rather than as a series of independent radiating units and the transfer- 
ence of a muscle from one digit to another is consequently a simple 
matter. 
9. The adductor pollicis—This seems to be the only representative of 
the deeper stratum of the flexor brevis medius which exists in the human 
hand. Its limitations have already been discussed in considering the 
flexor brevis pollicis and as a result of the conclusions then reached it is 
necessary to regard the muscle as consisting of two portions which have 
been termed the adductor obliquus and the adductor transversus. This 
nomenclature imples, however, the existence of two distinct muscles, 
4 This last argument is based upon the arrangement of the muscles which I have 
found in the Virginian opossum. If in other forms a doubling of the fourth lumbri- 
cal should occur, then the argument would lose its value. 
