MUSCULAR SYSTEM OF THE RED HOWLING MONKEY 129 



M. rectus femoris: A long muscle arising by two heads from the 

 innominate bone and extending distally to the knee. A direct tendon 

 is laterally compressed and has a lineal origin from the anteace- 

 tabular tubercle to the top of the acetabulum (fig. 36). It is thicker 

 near the bone and after a short stretch gives origin to fleshy fibers. 

 On a side view the tendon appears triangular, with the base corre- 

 sponding to its origin and the apex to the continuation with the 

 muscle. The reflected tendon is larger and laterally covered along its 

 ventral margin by the direct tendon. Origin is from the cranial margin 

 of the acetabulum (fig. 36), from where it runs distally for about 2 cm 

 before being joined by the other head. The rectus femoris descends 

 along the front of the thigh, flanked by the two vasti and covering 

 the intermedins. Its fibers become tendinous near the knee and are 

 arranged in two layers: (1) A superficial and larger group forms a 

 short and rectangular tendon, most of whose fibers are inserted in the 

 apex and both sides of the upper patellar border, the rest pass in 

 front of this bone, beyond which they are firmly attached to the 

 tibial tuberosity as the robust patellar tendon (figs. 37, 38, 39). (2) 

 The deep group is smaller and forms a more reduced tendon which 

 receives the fleshy and tendinous fascicles of vastus lateralis laterally 

 and distally joins the vasti intermedins and medialis as they are in- 

 serted upon the patella and the articular capsule. 



Sirena (1871) describes the direct tendon as being internal (medial?) 

 to the external (lateral?) and reflected one. This is the reverse of my 

 observations. According to him, the whole quadriceps is very well 

 developed. 



Nerve supply: The direct tendon receives two twigs from the 

 femoral nerve, one of them very small, before joining the reflected 

 part. Another branch of the femoral enters the undersurface of the 

 rectus femoris at the junction of the upper and middle thirds. 



Function: It flexes the hip and extends the knee. 



Mm. vasti: M. vastus lateralis is the largest of all the components 

 of the quadriceps and, as its name implies, lies on the lateral side of the 

 thigh. Its fleshy fibers have an aponeurotic and bony origin. They 

 come from the anterior aspect of the lateral intermuscular septum in 

 front of the insertion of both the gluteus maximus and the short 

 bicipital head on this fibrous partition, and from the almost entire 

 lateral part and the upper fifth of the anterior femoral surfaces (fig. 

 40). The origin of vastus lateralis reaches the intertrochanteric line on 

 the ventral surface of the bone. These fascicles are all directed dis- 

 tomedially and contribute to cover the vastus intermedins. Those 

 closer to the limb axis reach the lateral border of both terminal 

 tendons of the rectus femoris. Further away, fibers become aponeurotic 

 before a similar insertion, and still more distal ones, with respect to 



