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4th and 5th digits. The 1st dorsal interosseous muscle is inserted 
only into the base of the first phalanx, which it abducts and flexes. 
It is not connected with the dorsal aponeurosis on the index finger. 
The second is inserted into the bases of the 1st and 2nd phalanges 
of the middle digit. The remaining muscles of the series find in- 
sertion into the bases of all three phalanges of their respective fingers. 
The insertion into the first phalanx is in all cases quite free from 
the dorsal aponeuroses, and is the principal flexor as well as the 
abductor of this phalanx. The tendons to the other phalanges run in 
the dorsal aponeurosis, and act as extensors of the 2nd and distal 
phalanges. I cannot agree with HEPBURN (13), who states his incre- 
dulity concerning the possibility of a muscle acting in two directions 
at right angles. The dorsal interossei — and only one portion of 
each — are the main factors both for abduction and flexion of the 
proximal phalanges of all the fingers. In performing these two 
movements the muscles act in different combinations. The dorsal in- 
terossei and the abductor minimi digiti, can be felt contracting. 
All do so on flexion or abduction of the 1st phalanx, and all save 
the first dorsal interosseous on extension of the 2nd phalanges. I could 
not find any distinction in the insertion of the two muscular bellies 
described by Hrppurn (13) in the case of these muscles. The 
‘sheath action’ of the dorsal aponeuroses is exercised in conjunction 
with the palmar interossei and with the slips of those dorsal interossei 
which obtain insertion into the base of the 2nd phalanx. 
The arrangement of tendons on the dorsum of the toes is similar 
to that on the fingers. Again a dorsal aponeurosis is to be found, 
in which run the extensor longus (corresponding with communis), 
extensor brevis (corresponding with the extensor indicis series) lum- 
bricals and interossei. The differences between the hand and foot 
interossei as regards the digits to which they run, are those described 
in all text-books. The extensor longus, extensor brevis, and plantar 
interossei are all inserted into the base of the second phalanges 
(except in the case of the great toe, which of course corresponds 
with the thumb). ‘The dorsal interossei are inserted into the 1st and 
2nd phalanges, and the slip inserted into the ist is the only one on 
each toe not connected with the dorsal aponeurosis. The lumbrical 
tendons run to the tibial side of the base of the distal phalanx of 
each of the four outer toes. The abductor minimi digiti again corresponds 
with the dorsal interossei. 
