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The generally accepted insertion of the lumbrical muscles is into 
the radial side of the dorsal expansion on the four fingers. In most 
cases the tendons of the 1st, 2nd, and 4th lumbricals do run up the 
radial sides of the dorsal aponeurosis of their respective fingers, but 
the 3rd requires special mention. In only 8 cases did I find this 
running up the radial side of the ring finger. In 9 cases it ran to 
the ulnar side of the middle finger, and in 15 it divided and took 
both these courses. Hence this last disposition is to be regarded as 
normal. The lumbricals are inserted into the bases of the distal 
phalanges of their respective digits, their action being to flex feebly 
the first phalanx, and extend the third. The ‘sheath’ influence of 
the dorsal aponeurosis is shown in the action of these muscles. With 
regard to the 4rd lumbrical, it is interesting to note that this muscle 
has a variable nerve supply, and the proportion of cases in which it 
goes wholly or in part to the middle finger agrees very well with that in 
which it receives its nerve supply wholly or in part from the median. 
In papio anubis, several lumbricals were found to have two slips 
of insertion, and this irregularity was occasionally found in the human 
subject. Such divergencies from the normal have been mentioned by 
CunnincHam (8), PıersoL (9) and Macatister (10). Froment found 
great irregularities in about 45°/, of cases (11). From these facts 
it would seem reasonable to suggest that the lumbricals had originally a 
double insertion, or perhaps even two muscles existed in each interosseous 
space. The function of the decadent slips has been taken on by the 
palmar interossei, for in papio anubis I found no slips from the latter 
muscles to the distal phalanges, such as I have found in man. 
My dissections lead me to confirm the accepted description of 
the disposition of the tendons of the palmar interossei. I do not, 
however, find the exact mode of insertion to be that usually described 
in textbooks. The tendons run up the lateral parts of the dorsal 
aponeuroses, and divide, being inserted into the bases of the second 
and distal phalanges. There is no attachment of these muscles to the 
first phalanx, (this agreeing with the observations of CRUVEILHEIR and 
Morgen (12),) but a slip runs to the lateral metacarpo-phalangeal liga- 
ments of the several fingers. This however, is too low to have any 
action on the phalanx, and I am inclined to regard it as a superior 
limit of the origin of the muscle rather than as an insertion. The 
palmar interossei are adductors and flexors of the first phalanx, 
and extensors of the 2nd and 8rd phalanges. 
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