THE MUSCULAR SYSTEM -20!
>44i describes a similar insertion in the Gibbon ; Hepburn (83) points out that the tendon divides into three in the Orang; and Sominer <491f describes a double insertion into the tifth metatarsa! in the Crorilla. Both peroneal muscles have synovial sheaths.
The gastrocnemius is less voluminous than in Maii, so there is no marked calf. In the Chimpanzee it arise? by two heads from the capsule of the knee-joint over the articular surfaces. The bellies are inserted into a median tendinous raphe, the inner belly slightly overlapping the external one. The lint tendon is implanted into the tendon of the soleus half an inch above the os calcis to form the tendo Achillis. The muscle is connected at its edges to the soleus. Fibres arise in addition from the posterior ligament of the knee-joint in the Orang. The Gibbon has a sesamoid bone in each head of origin. In the Gorilla the muscle is as in Man.
The soleus has no direct tibial origin, and is smaller than in Man. It arises from the posterior aspect of the head of the fibula and from the peroneal interniuscular septum in the Chimpanzee. The flat belly unites a short distance above the os calcis with the gastrocnemius to form the tendo Achillis. Between the tendo and upper part of the os calcis are a bursa and a pad of fat. In the Orang and Gibbon the attachment is much more oblique than in the Gorilla and Chimpanzee, which place the sole flat on the ground.
The plantaris is absent in the majority of Apes. In a Chimpanzee I observed it rising from the postero-lateral side of the external femoral condyle. Its long, very slender tendon is inserted into the tendo Achillis.
The popliteus is single and similar to that in Man in