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directing the tendons of the palmar muscles so that they may act as 
extensors of the second and distal phalanges. In fresh specimens, 
this independence between tendons and aponeurosis is readily demon- 
strable, and the latter easily removed, but greater difficulty is 
experienced with subjects which have been preserved, especially if 
injected with formalin. This is probably owing to the effect of for- 
malin on connective tissue. When the aponeurosis is removed, the 
‘tendons are seen to be usually quite separate. Only seldom have 
they any connection whatever with each other. 
The extensor communis is inserted into the dorsal aspect of the 
base of the second phalanx of each finger. Occasionally a small slip 
runs up with the other tendons to the base of the distal phalanx, 
but I have never found any insertion into the lateral ligaments of the 
metacarpo-phalangeal joint or the first phalanx. The action of this 
muscle is to extend the first phalanx. If the three phalanges are 
flexed and traction is made on the extensor tendon, a hyper-extension 
of this phalanx is the only result which can be obtained. If however, 
during the traction, the first phalanx is kept flexed, partial extension 
of the second phalanx can be effected. In all cases the only method 
of producing real extension of the two distal phalanges is by drawing 
on the lateral parts of the dorsal aponeurosis with its enclosed tendons, 
the explanation of which will be apparent from the following paragraphs. 
The extensor indicis and extensor minimi digiti are each inserted 
into the ulnar side of the dorsum of the bases of the 2nd and 3rd 
phalanges of their respective fingers. They extend both the 2nd and 
3rd phalanges. In series with these muscles are special extensors 
sometimes found passing to the middle and ring fingers. Maca.ister 
(3) describes these under the titles ‘extensor medii digiti’ and ‘extensor 
tertii digiti’, and Kurra (4) also draws attention to them. In certain 
cases these muscles are continuous with the extensor minimi digiti, 
or extensor indicis, as pointed out by Cunnineuam (5) and MACALISTER 
(6). These extra muscles arise in man, in common with the extensor 
minimi digiti, and are inserted into the 2nd and 3rd phalanges of 
the middle and ring fingers. In papio cynocephalus the whole of 
this series is found, arising as a single muscle, and giving four ten- 
dons. In certain anthropoid apes, Hepsurn (7) found conditions approxi- 
mating to this. In the human type usually described, the two middle 
tendons have disappeared. Frequently, however, one of them is left, 
whilst sometimes the process of involution is carried further, and the 
extensor indicis or the extensor minimi digiti is missing: 
