390 THE MUSCULAR SYSTEM. 
it internally. It is a fan-shaped muscle, the fibres of which, converging to the 
lesser sacro - sciatic foramen, give rise to several tendons which hook round the 
margin of the foramen (a bursa intervening), and after traversing the buttock, unite 
together to be inserted into a facet on the inner surface of the great trochanter 
of the femur above the digital fossa. 
In the pelvis the muscle occupies the lateral wall, covered by the parietal 
(obturator) layer of pelvic fascia, which separates it from the pelvic cavity above 
and the ischio-rectal fossa below. It is separated from the contents of the pelvis, 
above by the peritoneum and extra-peritoneal fat, below by the fat in the ischio- 
rectal fossa. The internal pudic vessels and nerve cross it in the outer wall of the 
fossa in a special sheath of the fascia. In the buttock the tendon is embraced by 
the gemelli muscles which are attached to its upper and lower margins. The tendon 
is crossed by the sciatic vessels and nerves, and les upon the upper and back part 
of the capsule of the hip joint. 
The gemelli muscles form accessory portions of the obturator internus. They 
are two 1n number, superior and inferior. 
The superior gemellus arises from the gluteal surface of the ischial spine and 
from the upper part of the margin of the lesser sciatic notch. It is inserted into 
the upper margin and superficial surface of the tendon of the obturator internus 
muscle, 
The gemellus inferior arises from the upper part of the gluteal surface of the 
ischial tuberosity and the lower part of the margin of the lesser sciatic notch. It 
is inserted into the lower margin and superficial aspect of the tendon of the 
obturator internus. 
The quadratus femoris arises from the outer margin of the ischial tuberosity, 
and is inserted into the quadrate line of the femur. The muscle is placed beneath 
the gluteus maximus, and is crossed by the sciatic vessels and nerves. Its origin is 
concealed by the hamstring muscles. Its deep surface is in contact with the 
obturator externus muscle and the small trochanter of the femur, a bursa inter- 
vening. Its upper border is separated from the inferior gemellus by an interval, 
containing the tendon of the obturator externus and the ascending branch of the 
internal circumflex artery. Its lower border is separated from the upper margin 
of the adductor magnus by the internal circumflex artery. The muscle is not 
infrequently fused with the adductor magnus. 
THE MUSCLES ON THE BACK OF THE THIGH. 
THE HAMSTRING MUSCLES. 
The muscles comprised in this series include the biceps, semitendinosus and 
semimembranosus. A part of the adductor magnus, already described, belongs 
morphologically to this group. 
The biceps flexor cruris (m. biceps femoris) has a double origin. (1) J¢s long 
head arises, in common with the semitendinosus, from the lower and inner facet 
upon the ischial tuberosity and from the great sacro-sciatic ligament. This head, 
after a union of two to three inches with the semitendinosus, forms a separate fleshy 
mass, which extends to the lower third of the thigh, to end in a tendon, joined by 
the short head of the muscle. (2) 7'e short head arises separately (1) from the whole 
length of the linea aspera and the upper two-thirds of the external supracondyloid 
ridge of the femur, and (2) from the external intermuscular septum for a corre- 
sponding extent. The upper limit of its origin is sometimes blended with the 
insertion of the lowest fibres of the gluteus maximus. The fibres of the short head, 
directed downwards, join the tendon of the long head, and the muscle is inserted 
(1) into the head of the fibula by a strong tendon, split into two parts by the long 
external lateral ligament of the knee-joint, and (2) along its posterior border, by 
transverse aponeurotic fibres which connect the tendon with the popliteal fascia. 
At its origin the long head of the biceps is concealed by the gluteus maximus. 
In the lower two-thirds of the thigh it is superficially placed, with the semitendi- 
nosus and semimembranosus on its inner side. It conceals the great sciatic nerve, 
