. 
J. Playfair MeMurrich ATT 
in our fundamental plan, but also the lumbricales and the tendons of 
the flexor sublimis which are representatives of the flexor brevis super- 
ficialis. Instead, therefore, of recognizing but three layers in the mam- 
malian hand we must, I believe, admit at least five. These five layers 
I would correlate with the reptilian layers as follows: | 
Reptilia. Mammalia. 
Fl. brevis superfic. str. supertic. 
Flex revi ficialis. 
Fl. brevis superfic. str. prof. Rese in seta 
Fl. brevis medii str. superfic. Lumbricales. 
Fl. brevis medii str. medius. 
Fl. brevis medii str. prof. \ EA EINT O2 
Fl. brevis profundus Fl. brevis profundus, 
Intermetacarpales Intermetacarpales. 
I say I would recognize “at least ” five layers, since there is a possi- 
bility, though it seems to be remote, that representatives of both the 
middle and deep strata of the flexor brevis medius may be present; 
this point may, however, be more satisfactorily discussed later on. 
The other two exceptions that I would take to Cunningham’s scheme 
concern his distribution of the individual muscles to the different 
layers. By failing to recognize the most superficial layer he has in- 
cluded certain marginal muscles which, I believe, properly belong to 
it, in his intermediate layer, 7. e., in the flexor brevis profundus, and 
others in his dorsal layer. Furthermore, his dorsal layer includes also 
muscles equivalent to portions of the flexor brevis profundus of the 
reptilian hand, there being in the mamimalia an intimate association 
of certain slips of the flexor brevis profundus with the intermetacar- 
pales to form the dorsal interossei. These questions again can be more 
satisfactorily discussed later. . 
The planes of separation of the mammalian layers are essentially 
the same as in the lower vertebrates. Although a marked rearrange- 
ment of the main nerve stems has occurred in the higher group (see 
my previous paper, 1903), vet, I believe, we are justified in assuming 
that the plane occupied by the deep branch of the ulnar nerve corre- 
sponds with that occupied by the nerve stems in the reptilia and, 
consequently, the two layers situated dorsal to this plane correspond 
to the similarly situated layers of the reptilia. Again, I have shown, 
I trust satisfactorily, that the tendons of the flexor profundus digitorum 
represent the deeper layer of ‘the amphibian palmar aponeurosis and 
the profundus tendons of the reptilia and thus serve to separate, to a 
certain extent at least, the superficial and middle layers. 
The flexor digitorum brevis superficiatis——In my paper on the phy- 
