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The Nerves and Muscles of the Leg 
2. Variation in the Nerves of Distribution. 
The frequency of this variation is indicated in Table XXIV. Only 
those charts are used for tabulation which were based on the more 
accurate dissections of the distribution of the nerves to the 
muscles. Most frequently the nerve to the obturator internus 
muscle furnishes a branch to the superior gemellus muscle 
while that to the quadratus femoris muscle furnishes a branch to 
the inferior gemellus muscle. Occasionally a separate branch passes 
from the sacral plexus to the superior gemellus muscle. In distal forms 
of plexuses the nerve to the quadratus femoris muscle may furnish 
branches to both gemelli muscles. Not infrequently the branch to the 
quadratus femoris muscle is continued into the proximal portion of the 
adductor magnus muscle. This condition has been described by Wilson, 
89. In one instance I have followed a branch to the M. obturator 
externus. 
VII. THE HAMSTRING MUSCLES. 
a. Hmbryonic Development. 
1. General Features. 
In an embryo 11 mm. long (Plate III, Fig. 1) two branches from the 
tibial portion of the sciatic nerve represent nerves to the hamstring 
muscles. They terminate in a mass of tissue on the plantar side of the 
femur. The more proximal of the two nerves represents the proximal 
branches to the long head of the biceps and the semitendinosus ; the more 
distal nerve, that to the distal part of: the semitendinosus and the long 
head of the biceps and to the semimembranosus and adductor magnus 
muscles. 
In an embryo 14 mm. long (Plate VIII, Fig. 1) the various muscles 
mentioned are distinctly differentiated. But a single nerve branch is 
given to the sciatic portion of the adductor magnus (at this period a 
distinct muscle not closely fused with the obturator portion) and to the 
semimembranosus. ‘To the semitendinosus and to the long head of the 
biceps proximal and distal branches are given. About the terminus of 
each motor nerve the muscle differentiation is best marked. The tendi- 
nous attachments at each extremity of the muscles are indefinite. Proxi- 
mally they fuse with the ischial blastema. 
In an embryo 20 mm. long (Plate VIII, Fig. 3) the muscles of this 
group are attached by tendons to the skeleton. The obturator and sciatic 
portions of the adductor magnus have become fused. 
