MUSCULAR SYSTEM OF THE RED HOWLING MONKEY 153 



Nerve supply: The tibial nerve gives a branch to each head in 

 the popliteal space. 

 Function : Flexion of the knee and plantar flexion of the foot. 

 M. soleus: This other muscle of the superficial dorsal crural 

 compartment arises from the posterior slope of the head of the fibula 

 by strong tendinous fibers (fig. 38). They give rise to the fleshy 

 bundles while expanding on the deep and proximal part of the belly. 

 The soleus appears now as a dorsoventraUy flattened structure which 

 joins the overlying gastrocnemius in the intermediate third of the 

 crus (fig. 44). A long tendon of Achilles is formed within the combined 

 muscle and is covered by fleshy fibers on its two surfaces all the way 

 down to the calcaneal tuberosity, from which it is separated by a 

 large bursa. Its insertion is on the plantar surface of the tuberosity. 

 Sirena (1871) explains that a delicate aponeurotic lamina develops 

 on the deep aspect of the triceps cruralis and attaches to the upper 

 and lateral margins of the tuberosity. The bursa thus forms between 

 this sheet and the main tendon. 

 Nerve supply: N. tibialis. 

 Function: Plantar flexion. 



M. popliteus: Origin is by an intracapsular round tendon from 

 the lateral epicondyle in front of the beginning of the lateral head of 

 gastrocnemius (fig. 40). It travels posteriorly in a groove marked 

 between the articular surface of the lateral condyle and the lateral 

 origin of the gastrocnemius. The tendon enters the dorsal compart- 

 ment of the leg by piercing the capsule. The fleshy fibers of the muscle 

 are now directed medially under the soleus and gastrocnemius, the 

 proximal ones quite horizontally and the distal with a sharp incUna- 

 tion toward the tibia. They form a large triangular mass before being 

 inserted on the posterior surface of this bone from the posterior border 

 of the medial epicondyle to the popHteal line (fig. 38). Along the 

 medial margin of the tibia the fibers of the muscle attach to the 

 medial intermuscular septum. Sirena (1871) describes the origin a 

 little bit differently but essentially the same from the lateral epicon- 

 dyle. He notes the large size of the muscle. 



Nerve supply: A fine branch of the tibial nerve. 

 Function: It flexes the knee and produces some rotation of the leg 

 on the joint to the extent that the Ugaments allow this displacement. 

 M. flexor digitorum flbularis: It is the largest of the muscles in 

 the deep dorsal crural compartment (fig. 46). The long belly arises 

 (fig. 38) by fleshy fibers from (1) almost the entire dorsal and medial 

 surface of the fibula, (2) by initially tendinous fascicles from the head 

 of the fibula in common with the soleus, (3) the lateral half of the 

 lower two-thirds of the interosseal membrane, and (4) the transverse 

 intermuscular septum. These fleshy bundles descend to the ankle, 



