J. Playfair McMurrich 431 
rounding the most lateral tendon similarly separate to form the slip 
for the fourth digit. The fibers surrounding the two remaining ten- 
dons arrange themselves in two bundles, one lying immediately above 
the other, which, with their tendons, eventually unite to form the slip 
for the third digit (Fig. 8, fdb*). I take the more dorsal of the two 
bundles to represent the flexor brevis superficialis str. profundum; the 
slip to the third digit being the only portion of it persisting. 
The flexor brevis digitorum has been taken to be the exact equiva- 
lent of the flexor sublimis digitorum of the arm, and on that basis has 
been regarded as primarily a crural muscle which has secondarily de- 
scended into the foot. If the homologies traced in the preceding pages 
be correct, there are no grounds for assuming a descent of the muscle 
from the crural region. It is from the beginning an intrinsic muscle 
of the foot. 
The abductor hallucis (Fig. 8, abh), and abductor quinti digiti (abV) 
likewise require but brief consideration. There seems no doubt but 
that they are equivalents of the correspondingly named muscles in the 
lower mammals and are therefore derivatives of the primary super- 
ficial plantar layer. 
In the case of the flexor brevis hallucts, however, the matter is more 
complicated. The conception of it as a single muscle, so constantly 
found in text-books, probably dates back to Albinus, 34, by whom it 
was thus described, and is sufficiently satisfactory to the anatomist who 
studies muscles through physiological spectacles. So soon as a morpho- 
logical basis is sought for the classification of muscles, this one loses 
its simplicity. Cruveilhier, 77, reserves the name flexor hallucis brevis 
for the more medial portion of the muscle, regarding the lateral por- 
tion as a part of the adductor, and in this he has been followed by 
Flemming, 87, and Gegenbaur, 92, as well as by Ruge, 78a, in his com- 
parative studies. Cunningham, 82, however, regards the two heads as 
representing the haJlucal portions of his intermediate laver, the layer 
to which the plantar interossei belong and which, in typical cases con- 
sists of a pair of muscles for each digit. 
From my own studies I am compelled to dissent from the interpreta- 
tion which Cunningham gives to the muscle and to side with Cruveilhier 
and Flemming in regarding it as composed of two distinct portions 
which belong to different layers. My reasons for this belief are based 
largely upon the results obtained from the studies recorded in the 
preceding pages, which seem to point to the morphological independ- 
ence of the two heads of the muscle. But confirmation of this view is 
