672 HUMAN ANATOMY. 



sion) they can be made to stand out with the tendon of the extensor proprius hallucis 

 between them ; to the outer side of the extensor longus digitorum tendon a slight 

 groove indicates the interval between that muscle and the peroneus tertius. The 

 latter — as a muscle peculiar to man and probably developing as a result of his assump- 

 tion of the erect posture — is not invariably present. Above, between the extensor 

 longus digitorum and the soleus, the peroneus longus makes a longitudinal elevation 

 shading off below — where the fieshy fibres become tendinous — into the flatter pero- 

 neus brevis. 



Posteriorly the swell of the calf is formed by the gastrocnemius, and its surface 

 markings are due to the peculiar arrangement of the fleshy and tendinous pordons of 

 that muscle. When the calf muscles are in action, as in standing on the toes, it will 

 be seen that the inner head is the larger and descends somewhat lower than the outer 

 head ; and the lateral borders of the soleus will be seen coming to the surface beyond 

 the lower part of the gastrocnemius and the tendo Achillis and showing as curved 

 eminences, of which the outer is the longer. 



5. The Ankle and Foot. — The bony landmarks have been described (pages 

 390, 396, 437, 449, 453). 



At the front of the ankle the extensor tendons are easily recognized. The 

 largest and most internal is that of the tibialis anticus ; then, in order, the extensor 

 proprius hallucis, extensor longus digitorum, and — when present — the peroneus ter- 

 tius. Beneath the tendons of the long extensor and just below the external mal- 

 leolus, the fleshy belly of the short extensor of the toes, filling the space between the 

 OS calcis and astragalus, can easily be felt as a soft swelling over the outer part of the 

 tarsal region, and is distinctly visible when in action. On either side of the tendi- 

 nous elevation, on a level with the fine of the ankle-joint and in front of each 

 malleolus, is a little depression. This is effaced when the capsule is distended 

 by effusion (page 451). The two fleshy masses on the inner and outer border of 

 the foot are due respectively to the abductor and flexor brevis hallucis and the ab- 

 ductor and flexor brevis minimi digiti. The dorsal interossei project upward slightly 

 between the metatarsal bones. The lines on the dorsum of the foot corresponding 

 to the various joints have been described (page 453). 



Behind the ankle and at the sides of the tendo Achillis — between it and the pos- 

 terior surfaces of the malleoli — are two concavities, of which the outer is the deeper. 

 In it the tendons of the peroneus longus and brevis may be felt, the latter the nearer 

 to the fibula. In the inner concavity lie, in order from the malleolus backward, the 

 tendons of the tibialis posticus, the flexor longus digitorum, and the flexor longus 

 pollicis. 



On the sole of the foot the abductors of the great and little toes show somewhat 

 on the surface, but the chief outlines are determined by the arch of the foot, the 

 strong plantar fascia, and the thick integument. The digital creases have but little 

 practical value. 



As the foot, taken as a whole, acts as a lever, and as the calf muscles are 

 attached to the heel, — the short end of such a lever, — it follows that the develop- 

 ment of these muscles will stand in some relation to the length or projection of the 

 heel. As a short lever will require the application of a greater force to produce 

 the same result than will a long lever, we find the most marked muscular develop- 

 ment of the calf associated with a short foot and a short heel, while a long foot and 

 a long heel are the usual concomitants of a poorly developed calf (Thomson). The 

 athletic feats of some runners with poorly developed calves may sometimes be 

 explained by observing the unusual length and projection of the heel. 



