MUSCULAR SYSTEM OF THE RED HOWLING MONKEY 133 



POSTPELVIC 



M. gluteus minimus: The smaller of the gluteal muscles is tri- 

 angular, and its fleshy, firm origin from the margin of the greater 

 sciatic notch and the sciatic spine corresponds to the base of the 

 figure. It occupies the distal part of the gluteal plane and the promi- 

 nence of the glenoid cavity (fig. 41). The belly passes in front of the 

 iliofemoral capsule to which it is connected by fibrous strands. Inser- 

 tion is on the ventral border of the trochanter major between the 

 gluteus medius above and the scansorius below (fig. 40). M. gluteus 

 minimus is separated from the piriformis by the sciatic trunk, the 

 gluteal and posterior femorocutaneous nerves, the pudendal nerve 

 accompanied by the internal pudendal vessels, and the nerve to the 

 gemelli and quadratus femoris. 



According to Sirena (1871), this muscle is better developed than 

 the other two glutei and very difficult to separate from the medius. 

 Its origin, insertion, and relations otherwise correspond with what 

 I found in the red howler. Waterman (1929) assigns a double origin 

 to m. gluteus minimus (see her figure 3) in Alouatta, from the distal 

 part of the acetabular border and the margin of the greater sciatic 

 notch. The former probably corresponds to m. scansorius as indicated 

 by Hill (1962). 



Nerve supply: A branch from the superior gluteal nerves enters 

 the muscle on its superficial aspect near the cranial border. 



Function: A medial rotator of the femur. 



M. gluteus medius: It is the largest of the three gluteal muscles, 

 although not very much more so than the maximus (fig. 41). Its 

 fleshy fibers originate from an extensive area which includes (1) the 

 entire gluteal plane, except for a small portion occupied by the scan- 

 sorius, and (2) the whole peripheral margin of this plane, except the 

 part corresponding to the sciatic notch and that of the acetabular 

 border taken up by the scansorius and tensor fasciae latae (fig. 36). 

 Additional fleshy fascicles are supplied from the gluteal aponeurosis 

 near the iliac crest. The voluminous belly is directed distally under 

 partial cover of the gluteus maximus and tensor fasciae latae. The 

 ventral margin, formed initially by tendinous fibers, is closely related 

 to m. scansorius, and the caudodorsal to the piriformis, as this muscle 

 leaves its origin and goes to the trochanteric fossa. The gluteus medius 

 can be clearly separated from these two neighboring bellies, although 

 some fibers of the piriformis join the gluteal tendon near the vertex 

 of the large trochanter. M. gluteus minimus is completely covered 

 by the medius. All bundles of the medial gluteus converge upon a 

 central band-like tendon, those coming from the laterally facing part 

 of the gluteal plane end on the dorsocaudal aspect and lateral margin 

 of the tendon; fibers from the rest of this plane (and these are by 



