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Or 
Charles R. Bardeen 
which extends high on the medial side of the deep surface of the muscle. 
Fibre bundles may also run from the calcaneus to the tuberosity of the 
fifth matatarsal and from this to the tendon of insertion. ‘The more 
lateral and distal fibre bundles are those least frequently developed. 
The nerve may be distributed either near the deep or near the super- 
ficial surface of the muscle. The former appears to be the case when the 
muscle is slightly developed. The chief muscle branches then extend 
across the middle third of the constituent muscle bundles near the deep 
surface. In case the caleaneo-metatarsal bundles are well developed a 
special branch may be sent to these. When the muscle is well developed 
the nerve enters the proximal margin of the muscle and its chief branches 
extend across the middle third of the more superficial muscle bundles 
finally terminating in those most distal bundles which lie on the lateral 
side of the fifth metatarsal. Other modes of distribution are also found 
but they agree in general features with those described. 
Flexor brevis and opponens digiti quinti.—Beyond the anlage of the 
abductor digiti quinti the lateral plantar nerve in the 14 mm. embryo 
(Plate IX, Fig. 4) lies superficial to an ill-defined mass of tissue in which 
no segmentation into muscles can be made out. In the 20 mm. embryo 
(Plate IX, Fig. 6) a nerve branch extends from the lateral plantar nerve 
to the base of the 5th metatarsal and near the tip of this two slightly 
defined areas of partially differentiated tissue probably represent the 
anlages of the two muscles under consideration. According to Schomburg 
the anlage of these muscles lies at first in the area between the 4th and 
5th metatarsals but for this statement I find no support in the embryos 
studied. According to Ruge, 78, and Schomburg, oo, the flexor brevis 
and opponens muscles arise from a common anlage which becomes later 
differentiated into the two muscles. 
In the adult a single nerve is commonly distributed across the middle 
third of the bellies of each muscle. 
Mm. interossei.mRuge, 78, called attention to the fact that the inter- 
osseous muscles with the possible exception of the first dorsal have a 
plantar origin and that later the dorsal interossei wander between the 
metatarsals to the dorsal surface. Schomburg, oo, has confirmed this 
observation and has also shown that the dorsal interosseous I is originally 
plantar in position. In later embryonic stages Schomburg describes the 
dorsal interosseous II as extending on the plantar surface somewhat like 
the plantar interossei while the plantar interosseus I shows a tendency 
to wander dorsally like a dorsal interosseous. 
The first signs of the interessei muscles which I have seen are ill-de- 
