466 The Phylogeny of the Palmar Musculature 
radial slip of the muscle of the index and the ulnar one of that of 
the minimus are larger than their fellows and the ulnar slip of the 
minimus becomes intimately associated with the ulnar portion of the 
flexor brevis superficialis which has been referred to above as forming 
the abductor minimi digiti. 
The intermetacar pales, as their name indicates, extend across between 
adjacent metacarpal bones (Fig. 1, 2m). They are consequently three 
in number and each has a somewhat oblique course across the inter- 
metacarpal interval in which it lies. A muscle takes origin from each 
side of the fourth metacarpal and extends distally to be inserted, the 
one into the radial side of the fifth metacarpal, and the other into the 
ulnar side of the third; the third muscle arises from the radial side of 
the third metacarpal and is inserted into the ulnar side of the second. 
In addition to these muscles, which are the hand muscles proper, 
there is in the third digit a strictly digital muscle, the «interpha- 
langealis, which arises from the palmar surface of the distal portion 
of the proximal phalanx and is inserted into the fibro-cartilage of the 
proximal interphalangeal joint of the digit. 
I have endeavored in this description to be as brief as possible, since, 
so far as the final object in view, namely, the phylogeny of the mam- 
malian hand muscles, is concerned, a minute account of the amphibian 
muscles seems unnecessary. What is of importance is a clear percep- 
tion of their definite arrangement in layers, and a word seems advisable 
with reference to the relation of these layers to other structures. For 
unless definite dividing planes marked out by other structures can be 
recognized it will be a matter of no little difficulty to homologize the 
layers found in higher forms with those occurring in the group now 
under discussion. 
In this connection one’s thoughts naturally turn to the nerves as 
offering possible guides, and to a certain extent they do. It is not, 
however, in the details of their distribution to the individual muscles 
that they are of value in this respect, but rather in their general course 
and distribution. I do not intend to discuss here the significance of 
nerve supply in the identification of muscles; I have already in a pre- 
vious paper (1903) referred to this question. I may say, however, that 
from what I have observed it seems clear to me that too much import- 
ance has been attached to the nerve trunks from which the various 
individual limb muscles are supplied. Authors have been too apt to 
assume that what is termed the ulnar nerve, for example, in one form 
is the exact equivalent of the similarly named nerve in another form, 
and have concluded either that equivalent muscles may have entirely 
