. / A' T1CULA TIONS. LIGAMENTS. 445 



3. Technical Name. Tibio-fibulo-astragaloid articulation. 



4. Osteological Units. Tibia, fibula, and astragalus. 



5. Snbdivisional Parts. Inner and outer malleoli, astragalus. 



6. Articular Surfaces. Named according to the general rule. 



7. Basis. A capsule lined by a secreting synovial membrane. 



8. Local Subdivisions. Anterior, posterior, internal, external. 



9. Strengthening Bands. None. 



10. Incorporated Tendons of Obsolete Muscles. None. 



1 1. Bony Limitations. Malleoli of tibia and fibula, and the os calcis. 



1 2. Nerve-supply. Anterior and posterior tibial, and internal saphenous. 



13. Blood-supply. Anterior and posterior tibial and peroneal arteries. 



14. Ligamentous Muscles. Tibialis anticus, extensor proprius hallucis, ex- 

 tensor communis digitorum, peroneus tertius, peroneus longus, peroneus brevis, 

 tibialis posticus, flexor longus digitorum, flexor longus hallucis, and the three 

 muscles inserted by the tendo Achillis. 



Give the attachments of the anterior ligament of the ankle-joint. (Fig. 317.) 



It is attached above to the malleoli of the tibia and fibula, to the tibia, and 

 to the anterior inferior tibio-fibular ligament ; below, it is attached to the neck of 

 the astragalus. 



Give the relations of the anterior ligament of the ankle-joint. 



Anteriorly, it is in relation with the anterior tibial nerve and vessels, and all 

 the muscles of the front of the leg ; posteriorly, with the synovial membrane 

 and a fatty mass of connective tissue. 



Give the attachments of the posterior ligament of the ankle-joint. (Fig. 317.) 



It is attached above to the external malleolus, the tibia, and the posterior in- 

 ferior tibio-fibular ligament ; below, to the posterior surface of the astragalus. 



Describe the internal lateral ligament. (Fig. 318.) 



It is called the deltoid ligament. It is attached above to the lower border 

 of the internal malleolus ; below, to the astragalus, the sustentaculum tali, and 

 the calcaneo-astragaloid ligament. Externally, this ligament is in relation with 

 the tibialis posticus and flexor longus digitorum muscles ; internally, with 

 the synovial membrane. 



Describe the external ligament of the ankle-joint. (Fig. 317.) 



It has three fasciculi, or bundles, two of which are horizontal and one ver- 

 tical. The anterior bundle extends from the fibular malleolus to the astragalus 

 in front ; the posterior bundle from the malleolus to the posterior surface of 

 the astragalus ; the middle bundle from the malleolus to the outer surface of 

 the os calcis. 



Give the relations of the external ligament of the ankle-joint. 



Externally, with the tendons of the peroneus longus and peroneus brevis 

 muscles ; internally, with the synovial membrane. 



Describe the movements in tJic ankle-joint. 



This joint is a hinge ; hence it has movement in two directions, as in ordinary 

 walking. If, however, you extend the foot fully, you will find considerable 

 lateral motion. Flex the foot to the fullest extent, and no lateral motion is pos- 

 sible. Study the diameters of the articular part of the astragalus, and also the 

 diameters of the intermalleolar slot, in which the astragalus works, and you will 

 see reason for free lateral mobility of the foot in extreme extension, in the differ- 

 ence in these diameters. 



What can you say of the synovial membrane of the ankle-joint .' 



It lines the ligaments, and is said by Morris to secrete more synovia than 

 any other synovial membrane. 



