PHYSIOLOGY, AND PATHOLOGY OF THE CHIMPANZEE. 359 



sheath ahnost to its insertion ; but the deep belly loses its sheath 

 on the dorsum of the foot, and is separated from the cuneiform 

 bone by a bursa. 



The extensor longus digitorum arises from the external condyle 

 of the tibia internal to the head of the fibula, the anterior border 

 of the head of the fibula, the antero-medial surface of the fibula 

 to within an inch of the malleolus, the anterior peroneal inter- 

 muscular septum to the same level, the fascia between it and the 

 tibialis anticus and the fascia over its upper half. The belly 

 passes through the lateral compartment under the annular 

 ligament, and divides into four slips. The second slip is thready, 

 but the others are well developed. The first slip divides into 

 two ; the medial one going to the dorsum of the second toe, and 

 the lateral one joins the second slip and runs to the third toe. 

 The third and fourth slips run to the fourth and fifth toes. The 

 slips form dorsal expansions over the metacarpo-phalangeal joints 

 and proximal phalanges, which are joined by the lumbricales, 

 interossei, and extensor brevis, except in the case of the fifth toe. 

 The actual insertions into the bones are as in Man. 



The extensor longus halhccis arises from the middle third of the 

 antero-medial surface of the shaft of the fibula, and from the 

 outer part of the interosseous membrane, postei'ior to the extensor 

 digitorum longus. The belly passes through the middle com- 

 partment under the anterior annular ligament, and continues as 

 a tendon round the inner surface of the entocuneiform. It runs 

 through the naviculo-metatarsal trochlea (text-fig. 36 B) and 

 reaches the dorsum of the metatarsal of the hallux. A dorsal 

 expansion is formed over the first phalanx, the proximo-lateral 

 part of which joins the tendon of insertion of the most medial 

 tendon of the extensor brevis digitorum. The rest of the tendon 

 has an expanded insertion into the base of the terminal phalanx 

 of the hallux and the capsule of the interphalangeal joint. 



The peroneus tertius is absent. 

 • The gastrocnemhos has two heads, but they arise more pos- 

 teriorly and distally than in Man, and from the capsule of the 

 knee joint instead of from bones. They spring from the capsule 

 over the articular surface. They are inserted into a median 

 tendiiious raphe, the inner belly slightly overlapping the external, 

 and extending more laterally. The flattened tendon joins the 

 tendon of the soleus, half an inch above its insertion into 

 the calcaneus, forming the tendo Achillis. The edges of the 

 muscle are firmly connected to the subjacent soleus. 



The plantaris arises lower down than in Man, from the postero- 

 lateral side of the external femoral condyle. The slender belly, 

 three inches long, passes under the latei-al belly of the gastro- 

 cnemius, and the very fine thread-like tendon has an expanded 

 insertion into the tendo Achillis close to the calcaneus. 



The soleus has no tibial origin, and is smaller than in Man. It 

 has a fleshy origin from the posterior aspect of the head of the 

 fibula, and an aponeurotic origin from the upper part of the 



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