Zooluyical Society. 227 



the spines of the sacrum by a strong but short aponeurosis which 

 soon becomes fleshy; the cameous fibres converge as they descend '^, 

 and pass into a thin aponeurosis at the lower third of the thigh : 

 this is closely attached to the muscles beneath {vastus externus and 

 cruraus), then spreads over the outer and anterior part of the knee- 

 joint, is inserted into the patella, and into the anterior process of the 

 head of the tibia. 



Owing to the great antero-posterior extent of the origin of this 

 muscle, its anterior fibres are calculated to act as a flexor, its pos- 

 terior ones as an extensor of the femur : all together combine to 

 abduct the thigh and extend the leg, unless w hen this is in a state 

 of extreme flexion, when a few of the posterior fibres glide behind 

 the centre of motion of the knee-joint. 



Sartorius. — Tlie origin of this muscle is proportionally as much 

 extended as that of the jDreceding, ■nnth which it is posteriorly conti- 

 nuous : it comes off aponeurotic, from the anterior and superior 

 margin or labrum of the ilium ; the fibres soon become fleshy, and 

 the muscle diminishes in breadth and increases in thickness as it de- 

 scends : it is inserted by short and strong tendinous filaments ob- 

 liquely into the anterior part of the tendon of the broad rectus, and 

 into the upper and anterior end of the tibia. Its insertion is parth' 

 covered by the internal head of the gastrocnemius. 



It bends and adducts the thigh, and extends the leg. 



Biceps flexor cruris. — This is a single muscle, corresponding with 

 the preceding in the characteristic modifications of its extended ori- 

 gin, in relation to the great antero-posterior development of the pel- 

 vic bones. It is exposed by the removal of the broad rectus. Orig. By 

 a broad and thin aponeurotic tendon, which at first is confluent with 

 that of the rectus, but soon becomes distinct. Ins. The fleshy fibres 

 converge as they descend along the back and outer j^art of the thigh, 

 and finally terminate in a strong round tendon, which glides through 

 a loop formed here principally by a splitting of the tendinous origin 

 of the gastrocnemius externus, and is inserted into the process on the 

 outside of the fibula one inch from its proximal extremity. By 

 means of the loopf 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. — Origin. From the side of the coccygeal ver- 

 tebrae, and from the posterior end of the ischium ; it crosses the 



* They are not divided into a superficial and deep layer, as in the Ostrich, 

 but form a simple stratum, as in the Cassowary. Meckel regards the rectus 

 as entirely wanting in the Cassowary, supposing the present muscle' to he 

 the analogue o( the glutceus maximus and tensor vagincB united. He says 

 that Professor Nitzch observed a like absence of the rectus femoris in the 

 Emeu. The muscle which these anatomists call the rectus in other birds, is 

 a strip of the crurceus, arising high up from the femur, and which in the 

 Ostrich takes its origin from the as pubis. 



t Which in the common fowl is formed chiefly by a hgament extended 

 from the back of the outer condyle of the femur to the head of the tibia. 

 Q2 



