490 The Phylogeny of the Palmar Musculature 
belongs to this last layer. Its exclusion from the adductor layer seems 
certain from its relations in lower forms, in which it is evidently a muscle 
arising volar to the profundus tendons instead of dorsal to them, and 
there seems to be no reason for supposing that this superficial origin has 
been secondarily acquired. I regard the muscle, therefore, as a second 
member of the flexor brevis superficialis. 
It is unfortunate that by the application of the terms flexor brevis 
to their intermediate layer the English authors have introduced a cer- 
tain amount of confusion into the nomenclature of the hand muscles, a 
confusion which becomes very evident in the perusal of Brooks’ paper 
(1886). For finding that the flexor brevis quinti digiti is not a member 
of the intermediate layer he prints its name throughout in inverted 
commas and reserves the title of “the true flexor brevis minimi digiti ” | 
for what he regards as the ulnar slip of the intermediate layer. It seems 
far preferable to reserve the designation flexor brevis for muscles which 
belong to the superficial layer, since, in the first place, this layer has 
long been spoken of in the lower vertebrates as the flexor brevis digi- 
torum, and, in the second place, we have for the members of the inter- 
mediate layer the long-established term interossel. 
3. The abductor quinti digiti—This muscle has been referred by 
Cunningham to his dorsal layer and regarded as the most ulnar dorsal 
interosseus. It seems to me that the relations of the muscle in the 
lower vertebrates strongly negative such a supposition and show it to 
be a derivative of the most superficial sheet of the hand musculature. For 
I take it that the mammalhan muscle is the equivalent of the abductor 
minim: digiti of the lacertilia, the continuity of whose origin with that 
of the flexor brevis digitorum is so striking. 
It is interesting to note that in the forearm the deeper layers of 
muscles, represented by the flexor profundus and the pronator quadra- 
tus, do not extend laterally beyond the lines of the radius and ulna, and 
that the deepest layer is more limited laterally than is the middle one. 
It is from the superficial layer, that farthest from the bones, that the 
marginal muscles, the flexores carpi radialis and ulnaris, are derived. 
Such an arrangement is just what might be expected, for it would seem 
natural that the layer farthest away from the bony axis should wrap 
itself to a certain extent around the axis at the sides, while the closer 
the relations of the layers to the bones the more their lateral extension 
would be limited. We may expect to find this same condition obtaining 
in the hand as well as in the forearm, and when in addition to this 
a priori argument we have that derived from the continuity of origin 
of the abductor with the flexor brevis digitorum, strong evidence is 
