J. Playfair MeMurrich_ 469 
species, since, owing to the development of intersecting tendinous bands 
in certain of the layers, whereby they had the appearance of being 
composed of a number of distinct slips, and, further, owing to the lack 
of distinct layers of fascia separating some of the layers, it was by no 
means easy to recognize the true significance of some of the muscles. 
As pointed out in my paper on the forearm flexors (1903), the super- 
ficial aponeurosis which covers the flexor brevis superficialis in the 
amphibia is wanting throughout the greater part of its extent in the 
reptilia, so that the muscle is exposed completely on the removal of 
the integument. On the other hand, one finds a strong aponeurosis 
beneath the flexor superficialis (Fig. 3, p), arising from the distal edge 
of the volar cartilage or ossification (Figs. 4 and 5, vc) and passing dis- 
tally to become the profundus tendons. This beyond question is com- 
parable to the aponeurosis which separates the middle and superficial 
layers in the amphibia and may therefore serve as one of the orienta- 
tion planes for the comparison of the muscles in the two groups, the 
position of the palmar nerves, which is quite as distinct and definite 
as in the amphibia, marking a second plane. The muscle tissue lying 
between these two planes may be compared with the amphibian flexor 
brevis medius, that immediately dorsal to the nerve layer to the amphi- 
bian flexor profundus, and, finally, more dorsally still the equivalents 
of the intermetacarpals should be found. 
Working on this basis one at once observes that the superficial and 
middle layers are much more complicated than in the amphibia. It will 
be remembered that in that group the lateral parts of each portion 
of the flexor brevis superficialis unite toward their insertion with the 
profundus slips and that a similar fusion of the slips of the medius and 
profundus occurs. This condition becomes in one sense emphasized 
in the reptilia in that slips separate from both the superficialis and 
medius to form distinct muscles and, indeed, distinct muscle strata, 
which unite with subjacent layers at their insertions, and it is accord- 
ingly possible to recognize in the flexor superficialis a stratum super- 
ficiale (Fig. 3, fbs.) and a stratum profundwm (fbs,,), and in the flexor 
medius a stratum profundum (fobm,) distinct from the rest of the 
layer. But this is not all, for on the development of the profundus 
tendons in the reptilia from the deep layer of the palmar aponeurosis, 
the superficial portions of the flexor medius, as I have already pointed 
out (1903), remain in association with these tendons, forming the equi- 
valents of the mammalian lumbricales, and we thus have a stratum 
superficiale (fbm,) as well as a deep one separated from the flexor 
medius, which may, accordingly, be described as consisting of three 
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