152 u.s. national museum bulletin 2 73 



Comparative anatomy of the postpelvic coxofemoral 

 GROUP. — Alouatta shares with Ateles (Bodini, 1965; Hill, 1962; 

 Klaatsch, 1900), Brachyteles (Hill, 1962) and Lagothrix (Bodini, 

 1965; Hill, 1962; Klaatsch, 1900) a bicipital biceps femoris and thus 

 contrasts with Cebus, in which the biceps has no short head but, on 

 the other hand, possesses a m. tenuissimus (Bodini, 1965; Klaatsch, 

 1900). Klaatsch (1900) regards this muscle as homologue to the caput 

 breve of the biceps. Bodini (1965) agrees with Sirena (1871) that the 

 hamstring musjles of the howler are strong flexors of the knee and, 

 I add, also extensors of the thigh. From Bodini's work, which is still 

 in progress (personal communication), I get the impression that 

 these extensors of the thigh are more developed in Alouatta than, at 

 least, in the spider monkey. This would indicate that the extension 

 of this part of the hind limb and the flexion of the knee in the howler 

 are functionally more important than in Ateles. 



Cruropedal Croup 



M. gastrocnemius: This two-bellied muscle extends between the 

 distal end of the femur and the calcaneus (fig. 44). A caput laterale 

 originates by tendinous fibers from the lateral epicondyle on a well- 

 marked impression found in this part of the bone above the popliteal 

 groove (fig. 40). Additional tendinous and fleshy elements come from 

 the portion of the articular capsule covering the back of the lateral 

 femoral condyle. The tendinous fibers spread out as a shiny aponeu- 

 rotic lamina in the upper fifth of the lateral half of this head. This 

 belly joins those of the other head and of the soleus to form a common 

 tendon whose attachment is on the posterior end of the calcaneus. A 

 caput mediale arises by tendinous fibers from the medial epicondyle 

 right below the attachment of m. adductor magnus (fig. 40), and 

 more laterally by fleshy fibers from the articular capsule covering 

 the medial femoral epicondyle. The tendinous elements expand over 

 the dorsal surface of the muscle for a longer distance than in the oppo- 

 site head. Insertion takes place on the calcaneus as described before. 

 A sesamoid develops within the tendinous origin of each belly from 

 each epicondyle. The two bellies are closely apposed along the axis 

 of the limb, but it is only beyond the intermediate level of the crus 

 that they fuse to form a single muscle whose fleshy fascicles extend 

 as far as the heel. The sural nerve passes between the two heads at 

 the distal angle of the popliteal space. The short saphenous vein, 

 collecting blood from as far as the dorsum of the foot, enters the 

 space at this same point and empties into the popliteal vein. The posterior 

 tibial nerve passes distally deep to the medial head and after m. 

 soleus has joined the gastrocnemius it runs under cover of the medial 

 border of the combined muscle. The gastrocnemius in Alouatta jusca 

 (Sirena, 1871) offers no difference. 



