636 HUMAN ANATOMY. 



(page 1773 ), which, descending in the canal, press against the thin fascia cribrosa and 

 may cause it to bulge forward. 



The part of the fascia lata lying to the outer side of the fossa ovalis, or the 

 saphenous opening, is known as the iliac portion (Fig. 530 j, which at the lateral 

 margin of the fossa ovalis, where the fascia cribrosa joins the fascia lata, is somewhat 

 thickened to form a curved band termed \h& fa/ciform process (margo falciformis). 

 The latter is prolonged downward, as the cornu inferius, to join the pubic portion 

 of the fascia lata, and upward, as the cornu superius, also termed the femo7'al liga- 

 ment or Hey s ligament, which is somewhat stronger and continued medially to join 

 the inner end of Poupart's and Gimbernat's ligaments. 



Septa of connective tissue are continued from the deep surface of the fascia lata 

 to the femur separating the various muscles of the thigh. Two are especially strong ; 

 one, the inter'nal interrmiscular septzini (septum intermuscularis medialis), passing to 

 the inner lip of the linea aspera, between the vastus internus and adductor magnus 

 muscles, and the other, the external ifiterimtscular septum (septum intermuscularis 

 lateralis), to the external lip between the short head of the biceps and the vastus 

 externus. To a certain extent these septa furnish surfaces of origin for some of the 

 adjacent muscles. 



(a) THE PRE-AXIAL MUSCLES. 



I. Biceps femoris. 2. Semitendinosus. 



3. Semimembranosus. 



These muscles are popularly known as the hamstring vinscles. 



I. Biceps Femoris (Figs. 608, 609). 



Attachments. — The biceps femoris takes its origin by two distinct heads. 

 The long head arises from lower and inner facet upon the tuberosity of the ischium 

 in common with the semitendinosus, while the short head arises from the whole 

 length of the outer lip of the linea aspera and from the adjacent septum intermus- 

 culare. The fibres of both heads are directed downward, and at about the knee 

 unite in a common tendon which passes behind the outer condyle of the femur 

 and is inserted into the head of the fibula, bifurcating to embrace the long external 

 lateral ligament of the knee-joint. Tendinous bands usually extend also from the 

 tendon to the outer tuberosity of the tibia. 



Nerve- Supply. — Both heads are supplied by the greater sciatic nerve. The 

 fibres for the short head, however, pass, by way of the external popliteal division of 

 the nerve, from the fifth lumbar and the first and second sacral nerves, while those 

 for the long head pass by the internal popliteal division, coming from the first, 

 second, and third sacral nerves. 



Action. — To extend the thigh and flex the leg. When the leg is flexed the 

 biceps will rotate it outward, and the long head acting from below assists in extend- 

 ing the trunk upon the hip-joints. 



Relations. — The common tendon of origin of the biceps and semitendinosus 

 is sometimes separated from the tendon of the semimembranosus by a bursa (bursa 

 m. bicipitis superior). More rarely a bursa is to be found between the tendon of 

 insertion of the biceps and the lateral head of the gastrocnemius, and almost con- 

 stantly a bursa (bursa m. bicipitis inferior) separates the tendon of insertion from the 

 fibular collateral ligament of the knee-joint. 



Variations.— The most important variations of the biceps are an occasional absence of the 

 short head and an extension of the insertion to the crural fascia. Roth these anomalies are 

 explained by the composition of the muscle, the two heads not only representing: two ori,c;inally 

 distinct muscles, but, as is indicated by the nerve-supply, the long head is a portion of the pre- 

 axial musculature of the thi.s:h, while the short head belon.e^s to the post-axial .2:roup. The com- 

 parative anatomy of the muscle shows that the short head is a modified representative of a 

 muscle belonging to the gluteal set, which extended from the caudal vertebras to the fascia of 

 the crus and has only secondarily become united with the pre-axial muscle, sharing in its 

 insertion. 



