430 The Phylogeny of the Plantar Musculature 
The flexor brevis digitorum presents little difficulty. It is clearly 
homologous with the main mass of the flexor brevis superficialis str. 
superficiale, and certain of the peculiarities it presents are explicable 
on the basis of the phylogenetic history of that muscle. Thus the fre- 
quent origin of the slp for the minimus from the plantar surface of 
the tendon of the long flexor is clearly a reminiscence of the signifi- 
cance of the tendon as a portion of the plantar aponeurosis, and it 
merely obscures the true relationship to regard the slip having such an 
origin as something distinct from what is usually regarded as the 
normal slip. 
Fic. 8. Transverse section through the foot of a human fetus of 9 cm. 
abh =abductor hallucis; abV abductor quinti digiti; ak —adductor hal- 
lucis; fbh and fbh’ = medial and lateral heads of flexor brevis hallucis; foV 
= flexor brevis quinti digiti; fdb—flexor brevis digitorum; flm—=tendon of 
flexor longus hallucis; ZJd@—=dorsal interosseus; Ip—plantar interosseus; 
7=lumbricalis; J-V = metatarsal bones. 
The stratum profundum of the flexor brevis superficialis is so evident 
a constituent of the plantar musculature both in the lacertilia and 
mammalia, that its occurrence in the human foot seemed more than 
likely. An examination of sections of a foot from a fetus of 9 em. 
revealed what I take to be its representative. Before the flexor brevis 
begins to divide into its terminal slip, tendons appear imbedded in the 
center of the muscle mass, and of these, in the foot in question, there 
were four, notwithstanding the fact that the tendon for the fifth digit, 
as is so often the case, was derived from the tendon of the long flexor. 
The muscle fibers surrounding the most medial tendon gradually sep- 
arated from the rest to form the slip to the second digit, and those sur- 
