418 The Phylogeny of the Plantar Musculature 
digiti; but just opposite the insertion of the latter muscle it bends dor- 
sally (Fig. 3, /p), passing between the terminal portion of the abductor 
on the one side and the hallucal long flexor tendon and slip of the flexor 
brevis superficialis in the other, giving off at the same time two branches. 
One of these remains superficial and is continued along the medial border 
of the fifth digit, while the other passes dorsally with the main stem of 
the nerve and then bends medially to be supplied to all the slips of the 
flexor brevis medius str. superficiale except that which passes to the 
hallux. The main stem when it reaches the interval between the flexor 
brevis medius str. profundum and the flexores breves profundi (Fig. 4) 
makes an abrupt bend and passes medially as far as the line of the second 
metatarsal, passing dorsal to the main stem of the medial plantar. 
Without going into details regarding the various branches given off by 
the nerve in this deep portion of its course, it may be said that it sup- 
plies all the portions of the flexor brevis medius and flexor profundus 
layers except those which pass to the first digit, and that its cutaneous 
distribution is limited to the fourth and fifth digits. 
This condition is very different from what cccurs in Amblystoma, in 
which the medial plantar has the major supply of the pes. It would 
seem that there has been a shifting of fibers from the profundus to the 
fibular superficial stem, so that muscles originally supplied by the former 
are, in the lacertilia, supplied by the latter, and it is interesting to note 
that the transference has taken place to a much greater extent in con- 
nection with the motor fibers than with the cutaneous ones, so that the 
sensory supply of the medial plantar extends to digits where muscles are 
entirely supplied by the lateral plantar. 
In making a comparison between the muscles of the urodele and 
lacertilian it is evident that the nerve supply fails to give any criterion 
for homology and there is left only the evidence from topographic rela- 
tions. This, however, yields results which seem conclusive. 
The homologies may be briefly stated in the form of a table, no dis- 
cussion seeming to be necessary except in regard to the flexor brevis 
medius. In this muscle, as has been noted, there are two layers in the 
lacertilia, while only one was recognized in the amphibia. There seems 
little room for doubt, however, that indications of the double layering 
exist in the urodeles, each slip of the medius in these forms dividing into 
a more tibial and smaller portion and a larger fibular portion. These lie 
practically side by side and therefore do not represent exactly the con- 
dition in the lacertilia, but nevertheless it seems probable that the tibial 
