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anterior part of the tendon of the broad rectus, and into the anterior and inner part of 
the head of the tibia. Its insertion is partly covered by the internal head of the gastro- 
enemius. 
It bends and adducts the thigh, and extends the leg. 
The homologue of the Biceps flexor cruris (Pl. X. XI. x) is a unicipital muscle, cor- 
responding with ,the rectus extensor in the characteristic modification of its extended 
origin, in relation to the great antero-posterior development of the pelvic bones: it is 
exposed by the removal of the rectus. Orig. By a broad and thin aponeurotic tendon, 
which at first is confluent with that of the rectus but soon becomes distinct, from the 
posterior prolongation of the ilium: there is no second head from the femur. Ins. The 
fleshy fibres converge as they descend along the back and outer part of the thigh, and 
finally terminate in a strong round tendon, which glides through a loop (a) formed, as 
in the common Fowl, Ostrich, &c., by a ligament extended from the back of the outer 
condyle of the femur to the head of the tibia, and is inserted into the process on the out- 
side of the fibula one inch from its proximal extremity. By means of the loop the weight 
of the hinder parts of the body is partially transferred, when the leg is bent, to the 
distal end of the femur; and the biceps is enabled, by the same beautiful and simple 
mechanism, to effect a more rapid and extensive inflection of the leg than it otherwise 
could have produced by the simple contraction of its fibres. 
Semimembranosus (Pl. XI. XIV. 1).—Origin. From the side of the coccygeal vertebre, 
and from the posterior end of the ischium ; it crosses the superficial or internal side of 
the semitendinosus. Ins. Into the fascia covering the gastrocnemius and the inside of the 
tibia: through the medium of the fascia it acts upon the tendon (r*) of the internal 
gastrocnemius. 
Semitendinosus (Pl. XI. XIV. m).—This muscle arises from the posterior and outer 
part of the sacrwm and the aponeurosis connecting it with the ischium: it is a flattened 
triangular muscle, which receives the square accessorius muscle (nN) from the lower and 
posterior part of the femur. It gradually diminishes as it descends, and having passed 
the knee-joint, sends off at right angles a broad and square sheet of aponeurosis, which 
glides between the two origins of the gastrocnemius internus, and is inserted into the 
lower part of the angular ridge continued from the inside of the head of the tibia. The 
terminal tendon, continued from the apex of the muscle, then runs along the outer or 
fibular margin of the internal head of the gastrocnemius, and becomes confluent with the 
tendon of that muscle at r* Pl. XIV. 
Crureus (Pl. XI. XIV. 0),—This is a simple but strong muscle: it commences at the 
upper and anterior part of the thigh by two extremities, of which the outer and upper 
one, representing the vastus externus, has its origin extended to the base of the tro- 
chanter ; the inner and inferior comes off from the inner side of the femur, beneath the 
insertion of the gluteus magnus ; the two portions blend into one muscle much earlier than 
in the Ostrich. Ins, By the ligamentum patellee into the fore-part of the head of the tibia. 
I 
