PRACTICAL CONSIDERATIONS : ANKLE AND FOOT. 667 



munis and peroneus tertius, the last two running in one sheath. Internally — i.e., 

 between the heel and the internal malleolus — the tendons of the flexor longus pol- 

 licis, the flexor longus digitorum, and the tibialis posticus run beneath the internal 

 annular ligament, the last named being the deepest and in the closest proximity to 

 the ankle-joint, disease of which may originate in the tendon. The relation of the 

 flexor longus pollicis tendon to the posterior ligament is intimate, and is believed to 

 be of advantage in resisting posterior luxation of the astragalus (page 450). 



The peroneus longus tendon is thought to be more frequently displaced than 

 any other tendon in the body. When this accident happens, the tendon slips from 

 its groove behind the external malleolus and over the thin posterior border of the 

 latter to its anterior face. This dislocation is favored by (^a) the length and slender- 

 ness of the tendon ; {b^ the shallowness of the groove in which it runs ; (<:) the 

 relative weakness of the single slip of the external annular ligament that covers the 

 tendon; (a?) the fact that it changes its direction twice between the lower third of the 

 leg and its insertion, — i.e. , once at the malleolus and once at the margin of the cuboid. 



Disease of the sheaths of the tendons about the ankle-joint is not rare, is apt to 

 be tuberculous, and is favored by the frequent strains and the exposure to cold and 

 wet to which they are subjected, and by their dependent position and remoteness 

 from the heart. 



Their relation to disease of the tarsal bones should be remembered (page 437). 

 The approximately vertical direction of the swelling in the early stages is some- 

 times of use in differentiating teno-synovitis from ankle-joint disease (page 451). 



The involvement of the tendon-sheaths in sprain of the ankle-joint (page 450) 

 adds to the duration of the disability produced by that accident. 



On the sole of the foot the dense plantar fascia is of importance in relation to 

 infection or suppuration beneath it. Of its three divisions (page 659), the central 

 one is much the strongest. With the intermuscular septa that run from its lateral bor- 

 ders into the sole and separate the flexor brevis digitorum from the abductor minimi 

 digiti externally and from the abductor hallucis internally, it makes a compartment 

 the floor of which is rarely penetrated by inflammatory or purulent effusions. An 

 abscess beginning in the mid-region of the sole beneath the plantar fascia may pass 

 forward between the digital slips or upward through the interosseous spaces, or 

 along the tendon-sheaths to the ankle. More rarely apertures in the plantar fascia 

 permit suppuration to spread through it to the subcutaneous region of the sole. 

 The abscess cavity then consists of two portions connected by a narrow neck, abces 

 en bouton de chemise (Tillaux). 



The lateral progress of such an abscess — through the intermuscular septa above 

 described — is easier than penetration of the strong central leaflet of the plantar fascia. 



It will be noted that the three compartments into which the sole is then divided 

 are analogous to the thenar, hypothenar, and central divisions of the palm. Con- 

 traction of the plantar fascia, which aids in maintaining the curve of the arch of the 

 foot, as a string would that of its bow, increases that arch, is often associated with 

 the different forms of talipes, and is thought to be one of the common causes of a 

 subvariety, — pes caviis. Relaxation or elongation of the plantar fascia favors depres- 

 sion of the normal arch, and hence contributes to the development of the condition 

 known as "flat-foot" {pes pla?iiis) {vide infra). 



Club- Foot. — The mechanics of the normal foot have already been sufificiently 

 described (pages 436, 447). * 



Of the deformities, either congenital or acquired, which are grouped under the 

 name club-foot, it is necessary to describe, from the anatomical stand-point, only the 

 chief varieties. 



I. Talipes equino-varus, when congenital, is believed to result from retention 

 of the foetal position, — i.e., from defective development. The inward rotation of the 

 flexed and crossed limbs in idero, which in the later periods of foetal life removes the 

 pressure from the fibular side of the legs and the dorsum of the feet and puts the 

 latter in the position of extreme flexion with the soles — instead of the tops — of the 

 feet against the uterine walls (Berg), does not take place. This is the commonest 

 of all the forms of club-foot. When it is acquired, it may be due to paralysis of 

 those muscles that oppose the adduction and extension of the foot, — i.e., chiefly of 



