472 The Phylogeny of the Palmar Musculature i 
sections as a thin layer (Fig. 3, fbs,,) which separated from the dorsal 
surface of the str. superficiale almost opposite the junction of the 
proximal and distal halves of the metacarpals and passed distally to 
each of the three middle digits, lying dorsal to the slhps of the super- 
ficial stratum and becoming closely associated with the slips of the 
stratum superficiale of the middle flexor near their insertion. 
The portion pertaining to the second digit is quite slender and hes 
entirely upon the ulnar side of the digit; that for the third digit is 
stronger, however, and forms two slips passing one to either side of 
the digit, and the portion for the fourth digit also divides into two 
terminal slips between which a thin band of small-fibred muscular 
tissue extends forming, when the slips unite with the subjacent slips 
of the flexor medius, a complete sheath for the profundus tendon. 
It seems probable that a representative of this stratum also occurs 
in connection with the first digit, a portion of the flexor superficialis 
coming into relation near its insertion with the pollical portion of the 
flexor medius; it was not, however, quite distinctly separated from the 
general mass of the superficiale. In the case of the fifth digit the 
existence of a stratum profundum slip was much more evident, but 
on account of its intimate association with the minimal slp of the 
flexor profundus it will be more convenient to consider it later in 
connection with that muscle. 
The flexor digitorum brevis medius.—The stratum superficiale of the 
flexor medius arises from the dorsal surface of the palmar aponeurosis 
just where it divides to form the profundus tendons; the portion for 
the fifth digit forms an exception to this statement, since it arises 
rather from the surface of the stratum medium. The stratum consists 
of four thin band-like portions which pass to the four ulnar digits, 
there being no portion for the pollex. The portion for the index is 
very narrow and is completely concealed by the profundus tendon; in 
Iguana it passes to the ulnar side of the digit, but in Liolepisma it 
divides into two terminal slips which insert into either side of the base 
of the proximal phalanx. The portions for the medius and annulus 
are broader and each divides into two terminal slips which insert into 
either side of the digit, the annular portion being associated through- 
out a considerable part of its course with the corresponding portion 
of the deep stratum of the flexor brevis superficialis. 
The portion for the minimus (Fig. 4, fbm§) differs somewhat from 
the other three, as already stated, in arising from the thin fascia cover- 
ing the volar surface of the stratum medium. It has a very oblique 
direction, its origin being over the proximal portions of the second 
