Oo 
Charles R. Bardeen Su! 
branches of the sciatic nerve are tabulated and there is shown the fre- 
quency with which the different combinations occurred in 34 plexuses. 
From this table it may be seen that the nerve to the proximal segment 
of the semitendinosus muscle is most frequently the first of these branches 
to arise. Very frequently this branch is associated with one or both of 
the branches distributed to the long head of the biceps. Often the latter 
branches are the first to arise from the sciatic nerve. Rarely the branch 
to the distal segment of the semitendinosus arises in common with that 
to the proximal segment. When the most proximal branch given off is 
that to the proximal segment of the semitendinosus the next branch is 
usually that to the long head of the biceps. The more distal of the 
branches to the long head of the biceps may arise low down from the 
sciatic nerve. ‘The nerve to the distal segment of the semitendinosus 
arises about on the level and often in common with the nerve to the 
adductor magnus and semimembranosus. 
VIII. PERONEAL MUSCLES. 
a. Embryonic Development. 
During the sixth week the anlage of the peroneal muscles becomes sep- 
arated from that. of the long extensors of the toes and the tibialis an- 
terior (Plate IX, Fig. 1). Between the two anlages runs the n. peroneus 
superficialis. The anlage of each peroneal muscle begins at the same 
time to become distinct. Schomburg, oo, has described a connection in 
early embryonic development between the peroneus brevis and the ex- 
tensor digitorum brevis. In the embryos of corresponding stages which 
I have examined the two muscles are distinctly separated as shown in 
Plate IX, Fig. 1. 
The m. peroneus longus occupies the more proximal and superficial 
position. It lies dorso-lateral to the upper end of the fibula. Its proxi- 
mal extremity is some distance from the tibia. The distal extremity is 
continued into a tendon which can be followed to the neighborhood of the 
base of the fifth metatarsal where it is lost in tissue not yet distinctly 
differentiated. 
In somewhat older embryos the tendon of the muscle may be followed 
as it develops across the sole of the foot toward the base of the first 
metatarsal. In an embryo 20 mm. long the tendon is intimately fused 
with the scleroblastema of the foot and can be distinctly followed only 
partially across the sole. In an embryo 30 mm. long the tendon can be 
followed to the first metatarsal, but it is considerably later than this when 
the tendon becomes free in its sheath. In an embryo 14 mm. long, 
