J. Playfair McMurrich 425 
from the medial surface of the sheath enclosing the long flexor tendons, 
and also from the base of the second metatarsal. It passes distally par- 
allel with the hallucal slip of the flexor brevis superficialis, the long flexor 
tendon for the hallux lying between the two muscles, and is inserted into 
the lateral surface of the base of the first phalanx, a sesamoid cartilage 
being developed in its tendon. It is supplied by the deep branch of the 
lateral plantar nerve. In the cat and the mouse the muscle does not 
occur, unless it be represented in the mouse by a few scattered muscle 
fibers which occur in new born animals between the hallucal slips of 
the flexor brevis superficialis and the flexor brevis medius str. profundum. 
This is the muscle which Coues, 72, and Cunningham, 82, describe as 
the lateral head of the flexor brevis hallucis associating it with the 
hallucal slip of the flexor brevis superficialis, the latter author referring 
both slps to his intermediate layer (7. e., the flexor brevis profundus). 
Ruge, 78a, on the other hand, regards the muscle as distinct from the 
flexor brevis superficialis slip and refers it to his layer of contrahentes 
(1. e., to the flexor brevis medius str. profundum). I shall have occasion 
to consider this muscle or rather its human equivalent in connection with 
the human flexor brevis hallucis and shall remark concerning it here 
only that it occupies a plane ventral (7. e., plantar) to that of the hallueal 
portion of the flexor brevis medius str. profundum (Fig. 6) and that this 
fact, together with its innervation from the lateral plantar nerve and the 
relations of what is apparently the corresponding muscle in the lacertilia, 
lead me to consider it a portion of the superficial layer of the flexor brevis 
medius. 
The flecor brevis medius stratum profundum is formed by what are 
usually known as the adductors or, as they have been termed by Ruge, 78a, 
following Bischoff, 70, the contrahentes. In the opossum they are four 
in number. The two muscles which pass respectively to the hallux and 
minimus (Fig. 6, fom, ’) are large fan-shaped structures which arise 
from a median tendinous raphe extending from the base of the third 
metatarsal to the base of the proximal phalanx of the third digit, the 
fibers converging from this raphe on the one side to the base of the proxi- 
mal phalanx of the hallux and on the other to the base of the proximal 
phalanx of the minimus. The other two muscles are almost concealed by 
those just described, beneath which they lie, taking their origin from the 
dorsal surface of the tendinous raphe and passing distally to be inserted, - 
the one into the fibular side of the base of the second digit and the other 
into the tibial side of the base of the fourth digit. All four muscles are 
supplied by branches from the deep branch of the lateral plantar nerve. 
