MUSCULAR SYSTEM OF THE RED HOWLING MONKEY 151 



The caput breve has a double origin: (1) Its proximal fibers arise from 

 the dorsum of the lateral intermuscular septum below the middle of 

 the thigh. This membranous origin was described by Klaatsch (1900) 

 as taking place from the gluteal fascia. (2) As we approach the knee 

 the short bicipital fascicles come from the lateral supracondylar line 

 down almost to the corresponding condyle (fig. 40). Most fibers of 

 septal origin soon join the deep aspect of the long biceps and, as 

 pointed out by Klaatsch (1900), their respective fibers are to be differ- 

 entiated more by their direction than by a real division between one 

 caput and the other. The rest of the short bundles run distally, deep to 

 the longus tendon, to end by blending with the crural aponeurosis over 

 the proximal fourth of the leg, where its thin fibers form a weak 

 trigonum subtendinosum (fig. 39). 



Nerve supply: The short head receives a branch from the peroneal 

 nerve low down in the popliteal region. The long head is supplied by 

 a ramus of the tibialis nerve which also innervates the other postpelvic 

 ventral muscles of the thigh. 



Function: The caput longum is an extensor of the hip and a 

 flexor of the knee, where it also acts as a lateral rotator. The caput 

 breve flexes the knee. 



M. semitendinosus: The long semitendinosus extends from the 

 ischium to the medial side of the knee and the tibia. It has a common 

 origin with the caput longum biceps femoris from the lateral surface 

 of the ischial body (fig. 36). A muscular mass arises here on the rear 

 part of the distal border and after a short distance the two muscles 

 separate, the semitendinosus following a distomediad direction covers 

 the semimembranosus and forming the medial margin of the popliteal 

 space (fig. 44). On reaching the medial side of the knee, it is contained 

 together with m. gracilis within a common aponeurotic compartment; 

 it then expands and is inserted on the medial surface of the tibia as 

 the deepest muscle of the pes anserinus (figs. 37, 38). 

 Nerve supply: N. tibialis. 



M. semimembranosus: This muscle extends from the ischium to 

 the medial side of the knee joint. Origin is by tendinous fibers on the 

 femoral surface of the lower ischial ramus deep to the fascicles of 

 the ischiocondyloideus (fig. 36). The semimembranosus descends 

 under cover of the semitendinosus and passes behind the medial 

 epicondyle of the femur to be inserted by a robust, short, and flat 

 tendon on the medial tibial condyle under cover of the medial ligament 

 of the knee joint (figs. 37, 38). Some of its fibers pass toward the axis 

 of the femur at a right angle to the back of the articular capsule, 

 with which they are fused. 

 Nerve supply: N. tibialis. 



Function: These two muscles are extensors of the hip and flexors 

 of the knee. 



