J. Playfair McMurrich 427 
In the opossum there occurs in the interval between the first and second 
metatarsals a muscle (Fig. 6) which arises from the base of the first 
metatarsal and passes distally to be inserted into the tibial metatarso- 
phalangeal sesamoid cartilage of the second digit. In cross sections near 
its origin the muscle is distinctly seen to be composed of two portions, 
separated from one another by a tendinous partition, and the fibers on 
either side of the partition have a distinctly different direction. How far 
the presence of the partition and the difference in direction may be relied 
upon as an indication of a fusion of two primarily distinct muscles is un- 
certain, especially since towards their insertion the two portions fuse so 
as to be indistinguishable. J am inclined to believe, however, on the basis 
of comparison with lower.forms, that in this case the peculiarities do indi- 
cate a fusion and that the muscle really represents a flexor brevis pro- 
fundus hallucis and an intermetatarsalis I. 
Passing fibularly one finds over the second metatarsal two muscles 
again separated by a tendinous partition and also showing a very different 
direction of their fibers. These are evidently the flexores breves profundi 
II and they insert into the two sesamoid bones over the metatarso-phalan- 
geal joint of their digit, the more tibial one coming into relation with 
the combined flexor profundus I and intermetatarsalis I. Over the third 
metatarsal the arrangement is more complicated. Proximally one finds 
two muscle bundles lying side by side and separated by a tendinous parti- 
tion, but as one passes distally additional fibers, with a slightly different 
direction, become added upon either side, so that eventually four muscle 
bundles may be recognized over the bone (Fig. 6). The two lateral ones 
extend dorsally between the third and the adjacent metatarsals, while the 
two median ones, which are considerably smaller than the others, are con- 
fined to the plantar surface of the metatarsal. Eventually the plantar and 
lateral muscles of one side of the median line separate from the corre- 
sponding bundles of the other side, so that two pairs of muscles become 
recognizable which insert into the tibial and fibular metatarso-phalangeal 
sesamoid cartilages of the third digit. The two median bundles I take to 
be the flexores breves profundi III, while the lateral bundles are the inter- 
metatarsales IT and III. 
In the case of the fourth digit a determination of the arrangement is 
somewhat difficult, but just as muscles pass from the hallux to the second 
digit, so muscles from the minimus pass to the fourth digit, and it will 
therefore be convenient to consider the two digits together. In sections 
taken near the bases of the metatarsals two indistinctly separated bundles 
are to be seen over the third intermetatarsal space and a third one lies 
