422 The Phylogeny of the Plantar Musculature 
brevis hallucis to his intermediate layer (1. e., the flexores breves pro- 
fundi layer). The fact that both muscles are supplied by the medial 
plantar nerve and their apparent equivalency to the strong hallucal shp 
of the lacertilian flexor brevis superficialis lead me to regard Cunning- 
ham’s assignments as incorrect; they are due to the erroneous conception 
of the intrinsic muscles adopted by Cunningham. 
In the mouse, and to a greater extent in the cat, there is a reduction 
of the hallucal muscles owing to the reduction of the digit. In the mouse 
a muscle, supphed by the medial plantar nerve, arises from the navicular 
bone and is directed medially and distally to be inserted into the tibial 
side of the first phalanx of the hallux. It represents the hallucal slip 
of the flexor brevis superficialis, and in two out of three individuals 
studied was a single muscle. In a third individual, however, it had two 
heads, one from the navicular and the other, much smaller, from the 
tibial sesamoid bone which Baur, 85, has identified with the tibiale. The 
two heads eventually fuse, but it seems not improbable that the smaller 
one represents the abductor hallucis. 
In the cat the only representative of a superficial hallucal flexor seems 
to be the muscle named scapho-cuneiformis by Reighard and Jennings, 
or. It arises from the navicular bone and from the calcaneo-cuneiform 
lhgament and, in the individual studied, could be distinctly traced to the 
base of the rudimentary metatarsal. Reighard and Jennings describe it 
as inserting into the lateral surface of the first cuneiform; the difference 
may be due to my preparations having been made from an advanced 
fetus. The muscle is supplied by a branch from the medial plantar 
HETVes) © 
The fifth digit, in addition to a slip from the main mass of the flexor 
brevis superficialis, receives certain other superficial muscles which must 
be assigned to that layer. In the opossum there are three such muscles. 
One, for which Cunningham’s, 82, name abductor ossis metatarsi quintt 
digiti (Fig. 5, amV), may be adopted, has its origin from the lateral 
surface of the tuberosity of the caleaneus and passes distally, over the 
quadratus plant to be inserted into the lateral surface of the base of 
the fifth metatarsal. A second muscle (Fig. 5,abV), arises from the cal- 
caneus in close proximity to the preceding and over the base of the fifth 
metatarsal is continued into a slender tendon, which inserts into the lat- 
eral surface of the base of the proximal phalanx of the digit; while the 
third muscle (Figs. 5 and 6, abV’), takes its origin from the plantar 
surface of the sheath enclosing the long flexor tendons and passes distally 
and laterally to unite with the tendon of the second muscle near its 
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