JOINT OF THE ANKLE. 



is tipped with cartilage, and convex in the ver- 

 tical direction, being received upon a corres- 

 ponding concavity on the outer side of the 

 astragalus; upon the lower and back part of 

 this inner surface may be seen a deep depres- 

 sion, where the posterior fibulo-tarsal ligament 

 arises; the anterior edge of the malleolus is 

 sharp, and gives origin to the anterior fibulo- 

 tarsal ligament ; the posterior edge is marked 

 by a deep groove, whieh transmits the tendons 

 of the peronei muscles, longus and brevis. 

 The apex of the malleolus is below, and gives 

 origin to the middle fibulo-tarsal ligament. 



The astragalus enters into the formation of 

 the ankle-joint by its superior surface, and a 

 portion of its two lateral surfaces. On the 

 superior surface we observe, anteriorly, a well 

 marked groove forming part of the neck of the 

 astragalus ; into this groove the anterior tibio- 

 tarsal ligament is inserted. Immediately be- 

 hind the groove we meet with an articulating 

 eminence of an oblong quadrilateral form, an 

 inch and a half in its antero-posterior, and about 

 an inch and a quarter in its transverse measure- 

 ment; (this transverse measurement is, however, 

 a little greater in front than behind ;) the emi- 

 nence is remarkably convex from before back- 

 wards, and concave from side to side ; the outer 

 edge somewhat more elevated than the inner ; 

 it is completely covered with cartilage, and cor- 

 responds to the articulating cavity upon the in- 

 ferior exremity of the tibia. Upon the inner 

 side of the astragalus, we find a small articu- 

 lating surface of a triangular form, with the 

 base above and apex below; it is convex in 

 the vertical direction, and is tipped with car- 

 tilage prolonged ftom the superior surface: 

 upon thetriangular surface the internal malleolus 

 plays ; the remaining portion of the inner side 

 of the astragalus is rough, and occupied chiefly 

 by the insertion of the internal tibio-tarsal 

 ligament. The external side of the astragalus 

 is also marked by an articulating surface of a 

 much greater size for the reception of the ex- 

 ternal malleolus : it too is of a triangular form 

 with the base above ; concave in the vertical, 

 and slightly convex in the antero-posterior 

 direction. 



b. Ligaments. We have already compared 

 the mechanism of this joint to that of the tenon 

 and mortise ; the mortise cavity, however, is not, 

 as we have seen, cut out of a solid bone, but 

 teing formed in great part in the lower extremity 

 of the tibia, is completed on the outer, side by 

 the fibula, which is firmly united with the tibia 

 by strong ligaments, forming what is called the 

 i nferior tibw-fibulur articulation. We shall not 

 now describe the ligaments which here unite the 

 tibia and fibula, referring to the article on the 



TlBlO-FIBULAR ARTICULATION ; but W6 must 



observe that, however it may be advisable, in 

 anatomical descriptions, to separate this last 

 named articulation from the ankle-joint, they 

 are perfectly inseparable in their functions, the 

 integrity of the latter being essentially dependent 

 on that of the former : indeed it may be said, 

 that, by virtue of the great strength of the liga- 

 mentous connexion between the tibia and fibula 

 in the former articulation, the mortise is n* 



strong, nay, in some respects stronger, than if it 

 had been formed out of solid bone. 



The ligaments which connect the tenon and 

 mortise together, or to speak more literally, 

 which tie the tibia and fibula with the tarsus, 

 are five in number, namely, two tibio-tarsal 

 and three fibulo-tarsal ligaments. 



1 . The internal tibio-tarsal ligament is also 

 called the internal lateral, and by Weitbrecht 

 the deltoid ligament. There is, however, no 

 reason why we should not apply to it likewise 

 that principle of nomenclature which is so gene- 

 rally and with such advantage applied to other 

 ligaments. It arises by a truncated apex from 

 the point of the inner malleolus, and from the 

 little fossa at its outer surface ; its fibres change 

 as they proceed downwards and are fixed into 

 the inner surface of the astragalus and os calcis, 

 some proceeding as far forwards even as the 

 scaphoid bone. The posterior fibres are strong 

 but short ; the anterior are much larger and 

 not so thick. Its internal surface is lined by 

 the synovial membrane of the joint; and on its 

 internal surface it is covered by the tendon of 

 the tibialis posticus, and it sends some of its 

 fibres to the sheath of the flexor longus 

 digitorum tendon. In flexion of the leg the 

 anterior fibres are relaxed, and the posterior are 

 rendered tense: in extension the reverse of 

 course takes place. 2. The anterior tibio- 

 tarsal ligament (lig. tibio-tarsal, Cloquet) con- 

 sists of a few loose fibres scattered over the 

 synovial membrane, and in some instances so 

 delicate and so separated by pellicles of fat as 

 to be scarcely perceptible. They arise from 

 the fore part of the inner malleolus and the 

 adjacent anterior portion of the tibia, and de- 

 scend obliquely downwards and outwards to 

 be inserted into the neck of the astragalus. 

 This ligament is covered anteriorly by the ten- 

 dons of the tibialis anticus, extensor proprius 

 pollicis, and extensor digitorum longus : poste- 

 riorly it is in contact with the synovial mem- 

 brane. 3. The anterior fibulo-tarsal ligament 

 (lig.fibule anterius, Weitb., anterior external 

 lateral, Boyer) arises from the anterior edge of 

 the outer malleolus, a few lines from its ex- 

 tremity; it descends obliquely forwards and 

 inwards, and is fixed into the astragalus imme- 

 diately in front of the articulating surface which 

 receives the fibula: it is scarcely an inch in 

 length, of an oblong quadrilateral form, and is 

 frequently subdivided into two distinct parts. 

 In extension of the foot it is rendered tense ; 

 in flexion it is relaxed. 4. The middle fibulo- 

 tarsal ligament ( lig. fibula medium perpen- 

 diculare, Weitb., external lateral ligament, 

 Cloq.) is a round fasciculus of fibres having 

 almost the appearance of a tendon which arises 

 from the apex of the external malleolus, de- 

 scends obliquely backwards, and is attached 

 to the outside of the os calcis. It does 

 not appear to us that in any position of the 

 joint this ligament takes a perpendicular course, 

 although that epithet has been applied to it by 

 Weitbrecht. It is related superficially to the 

 peroneus longus tendon, and by its deep sur- 

 face to the synovial membrane, to the astra- 

 galus, and os calcis. In flexion of the foot this 



