J. Playfair MeMurrich 483 
in the reptilia. Certain possible elements of such a layer will be dis- 
cussed later in connection with the lumbrical muscles. 
The flevor digitorum brevis medius——As I have already stated, the 
_ stratum superficiale of this layer is represented by the lumbricales, 
arising from the tendons of the flexor profundus digitorum and passing 
to the four inner digits. 
In the reptilia it was noted that the portion of this stratum which 
passed to the minimus inserted only into the radial side of that digit, 
while the portions to the annulus and medius divided to pass to either 
side of the proximal phalanges. In the opossum (Fig. 7) one finds an 
Fig. 9. Transverse section of the hand of a new-born mouse. «ab°®, abductor min- 
imi digiti; ad.m, adductor minimi digiti; ad, p, adductor pollicis; ad*, adductor 
indicis; fb', flexor brevis pollicis; fb°*, flexor brevis minimi digiti; fbp,, and fop,,, 
radial and ulnar slips of the flexores breves profundi; 7, lumbricales; m, median 
nerve; p, tendons of the flexor profundus digitorum; s, tendons of the flexor 
sublimis digitorum; wp and ws, deep and superficial branches of the ulnar nerve. 
interesting suggestion of a similar arrangement, the lumbricals to the 
medius and annulus each consisting of two distinct portions, one large 
portion (/ and 7’) which inserts into the radial side of the proximal 
phalanx of its digit and a smaller one (lv and Ji). The smaller portion 
of the third lumbrical arises from the radial side of the fourth long 
profundus tendon and passes distally, retaining its independence 
throughout its entire course, to be inserted into the sheath enclosing 
the long tendon just where the sublimis tendon spreads out to allow 
its passage; the corresponding portion of the second lumbrical arises 
