J. Playfair MeMurrich 409 
fundi. The continuity is, however, probably merely an apparent one, the 
fibers of the flexor brevis superficialis beginning to arise from the plantar 
aponeurosis before those of the plantares profundi have completed their 
insertion, so.that there is a confusion of the two groups of muscles. The 
fact that one finds, first the continuous sheet of the plantares, then for a 
short distance three slender slips separated by portions of the plantar 
aponeurosis, and then again a continuous sheet of flexor brevis superfi- 
cialis, seems to indicate that one has to do with two distinct muscles, es- 
pecially when comparison is made with the arrangement in the hand, and 
when it is noted that the portions of the superficial flexor which pass to 
the marginal digits arise from the aponeurosis independently of the 
plantares, the portions continuous with these muscles passing only to the 
three central digits. 
Fic. 2. Transverse section through the metatarsals of the third and fourth 
digits of Amblystoma near their heads. fm and fm’—=central and lateral 
slips of flexor brevis medius; fp—slips of flexor brevis profundus; fs and 
fs’ central and lateral slips of flexor brevis superficialis; im = intermeta- 
tarsalis; pa— plantar aponeurosis; JJJ and /V = metatarsal bones. 
If the plantar aponeurosis and the flexor brevis superficialis be traced 
distally they will be found to split into as many slips as there are digits, 
the prolongations of the aponeurosis inserting into the terminal phalanges. 
In the muscle slips destined for the third and fourth digits the marginal 
portions (Fig. 2, fs’) separate and pass to an insertion into the sides of 
the heads of their metatarsals, these insertions being closely associated 
with those of the flexores breves profundi. A little more distally the 
central portion of each slip (fs) begins to undergo a transformation into 
connective tissue and gives rise to a tendon which applies itself to the 
dorsal surface of the slip derived from the plantar aponeurosis and fuses 
with it over the base of the first phalanx, the muscle fibers on either side 
of this central tendon inserting into the sides of the fibro-cartilages over 
the metatarso-phalangeal joint. 
