J. Playfair McMurrich 421 
The well developed slip of the flexor brevis superficialis which passed 
to the hallux in the lacertilia is represented in the opossum by two closely 
associated muscles. One of these, which may be termed the abductor 
hallucis (Fig. 5, ah), arises from the dorsal surface of the tarsal spur, 
over the base of the first metatarsal, and is inserted into the first phalanx 
in close proximity to the medial metatarso-phalangeal sesamoid cartilage ; 
the other, which may be designated the flexor brevis superficialts hallucis 
(Fig. 5, fbs’), arises in part from the dorsal surface of the tarsal spur, 
but more extensively from the sheath which encloses the tendon of the 
long flexor, the main portion of the flexor brevis superficialis and the 
medial plantar nerve, and is inserted into the medial metatarso-phalan- 
geal sesamoid cartilage. 
Fic. 5. Transverse section through the junction of tarsus and metatarsus 
in the opossum. abV and abV’=abductor quinti digiti; aa —=abductor hal- 
lucis; amV — abductor ossis metatarsi quinti digiti; cn. and cn,—second and 
third cuneiforms; cw—cuboid; fbs’—hallucal slip of flexor brevis super- 
ficialis; fds, — flexor brevis superficialis str. profundum; /f—tendon of flexor 
fibularis; ff—tendon of flexor tibialis; ts tarsal spur; 7, JJ, IV, and V= 
metatarsals. 
These two muscles, although closely associated, are separated by a dis- 
tinct sheet of connective tissue, and their fibers have a markedly different 
direction, so that in sections they are readily distinguishable. Consider- 
able differences of opinion have been expressed as to their significance. 
Coues, 72, failed to recognize the abductor as distinct from the more 
lateral slip, which he describes as a portion of the flexor brevis hallucis; 
Ruge, 78a, who fails to recognize two muscles, terming the combination 
the abductor hallucis; while Cunningham, 82, who does recognize the 
abductor, refers it to his dorsal layer (7. ¢., the intermetatarsal layer), 
while the flexor superficialis hallucis he assigns as part of the flexor 
