J. Playfair MeMurrich 473 
and third metacarpals, so that in its course to its digit it crosses 
obliquely over the medial and annular portions of the stratum medium. 
It is inserted into the radial side of its digit. 
The stratum medium (Fig. 4) is the thickest layer of the flexor 
medius, almost equalling the flexor superficialis in its development, 
It is divided by tendinous bands lying in the sagittal plane into a 
number of parts, several of which pass to each digit. The general 
mass sends a portion to each digit, that to the minimus (Fig. 4, fbm,;,) 
having an oblique direction, and overlapping at its origin the portions 
which pass to the fourth and part of that of the third digit. 
The stratum profundum consists of three distinct portions which arise 
in the fascia covering the dorsal surface of the stratum medium and 
pass to the radial side of the medius, index (Fig. 3, fbmj,) and pollex. 
At their origin these muscles lie distinctly in a plane palmar to that 
occupied by the main nerve trunks, but more distally the nerves come 
to he in the same plane as the muscles, so that from sections cutting 
the distal parts of the muscles it would be difficult to say whether 
they belonged to the flexor medius or the flexor profundus. Their 
relations at their origins, however, clearly show their true significance. 
The muscle which passes to the third digit has its origin over the 
ulnar edge of the third metacarpal, so that in its course to its insertion 
it passes somewhat obliquely toward the radial side. The same is also 
true for the other two muscles, that for the index arising over the 
ulnar border of the second metacarpal and that for the pollex over the 
middle line of the first metacarpal, its obliquity, however, being more 
pronounced than that of the other two muscles owing to its being 
inserted into about the middle of the radial surface of the metacarpal, 
instead of passing to the neighborhood of the metacarpo-phalangeal 
joint. 
The flexor digitorum brevis profundus.—The flexor profundus pre- 
sents some interesting peculiarities in the arrangement of its con- 
stituent muscles (lig. 5). In the amphibia it consisted of three slips, 
a median and two lateral, for each digit; in the reptilia almost the same 
condition obtains, but the median slip, except in the case of the mini- 
mus, is greatly reduced and is associated with one of the lateral slips 
and, furthermore, each radial lateral slip of the four ulnar digits, 
instead of being inserted into the digit from which it arises, passes 
obliquely across an intermetacarpal interval to be inserted into the 
ulnar side of the adjacent digit. 
In the pollex I find but one muscle that I can certainly refer to this 
layer (Fig. 3, fbp:). It arises from the first metacarpal and inserts 
