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THE MUSCLES ON THE BACK OF THE THIGH. aol 
the origins of the semimembranosus and quadratus femoris, the adductor magnus, 
and the short head of the muscle. 
boundary of the popliteal space, and 
partially conceal the outer head of 
the gastrocnemius. 
The short head may be absent: 
there may be an additional origin 
from ischium or femur; and the 
long head may send a slip to the 
gastrocnemius or tendo Achillis 
(tensor fascize suralis). 
The semitendinosus arises, in 
common with the long head of the 
biceps, from the lower and inner 
facet upon the ischial tuberosity. 
Separating from the common tendon 
after a course of two or three inches, 
the muscle forms a long narrow 
band which becomes tendinous in 
the middle third of the thigh. 
Passing over the inner side of the 
knee, it spreads out and becomes 
membranous, and is inserted into 
the inner side of the shaft of the 
tibia just below the internal tuber- 
osity, below the gracilis and behind 
the sartorius. A bursa separates it 
from the sartorius in front, and 
another, common to it and the 
gracilis, lies beneath its insertion. 
The origin of the muscle is 
concealed by the gluteus maximus. 
In the back of the thigh it is super- 
ficial to the semimembranosus ; and 
at the inner side of the knee the 
tendon lies behind that of the 
gracilis. It forms one of the inner 
boundaries of the popliteal space. 
The belly of the muscle is marked 
by an oblique septal intersection 
about its middle. 
The semimembranosus arises 
by a tendon from the upper and 
outer facet on the ischial tuberosity. 
In the upper third of the thigh the 
tendon gives place to a rounded 
fleshy belly, which, becoming ten- 
dinous at the back of the knee, is 
inserted mainly into the horizontal 
groove on the back of the inner 
tuberosity of the tibia. A bursa 
lies beneath the tendon at its 
insertion. It has three additional 
GRACILIS 
ADDUCTOR MAGNUS ~ 
SEMITENDINOSUS 
SEMIMEMBRANOSUS =< 
SARTORIUS TENDON 
The united heads assist in forming the outer 
PYRIFORMIS 
OBTURATOR 
INTERNUS AND 
A GEMELLI 
OBTURATOR 
EXTERNUS 
GLUTEUS 
MAXIMUS 
» QUADRATUS 
9 YEMORIS 
Great sciatic 
nerve 
ADDUCTOR 
MAGNUS 
Biceps (long 
head) 
Biceps (short 
head) 
Tibial nerve 
BICEPS TENDON 
(along with 
peroneal nerve) 
PLANTARIS 
= GASTRO- 
CNEMIUS 
Fic. 258.—THE Muscles ON THE BACK OF THE THIGH. 
membranous insertions: (1) a fascial band extends downwards and inwards to 
join the posterior border of the internal lateral ligament of the knee-joint; (2) 
another fascial band extends downwards and outwards, forms the fascia covering 
the popliteus muscle, and is attached to the oblique line of the tibia; and (3) 
another band extends upwards and outwards to the back of the external condyle 
of the femur, forming the posterior ligament of the knee-joint. 
