I38 ATLAS AND TEXT-BOOK OF HUMAN ANATOMY. 



Fig. 224. — The ankle-joint seen from behind (|). 



Fig. 225. — Horizontal frozen section through the tarsal articulations (f). 



Fig. 226. — Frontal frozen section through the ankle and posterior talocalcaneal joints (£). 



slight separation of the bones of the leg; and when the foot is depressed, the narrow posterior portion of the trochlea 

 has so much room in the articular socket that slight lateral movements are possible in the axis of the fibula. The ankle- 

 joint is consequently not a pure hinge joint, although it acts mainly as such; its movements are those of plantar and 

 dorsal flexion. 



The talocalcaneal articulation (Figs. 225 and 226) is the joint between the convex posterior 

 articular surface of the calcaneus and the concave posterior calcaneal articular surface of the 

 talus (astragalus). The articulating facets are portions of the surface of a cone, the axis of which 

 is almost sagittal, but directed somewhat obliquely upward and forward. The articular capsule 

 is roomy and relaxed. This articulation occasionally communicates with the ankle-joint. 



The talocalcaneo-navicular articulation (Figs. 225 and 230) is the joint formed by the head 

 of the (talus) astragalus, the anterior and middle articular facets of the calcaneus, the posterior 

 articular facet of the navicular, and the navicular fibrocartilage of the plantar calcaneonavicular 

 ligament (see page 141). The joint is a pronouncedly compound articulation, and includes an 

 anterior talocalcaneal and a talonavicular articulation. The socket for the head of the talus (astrag- 

 alus) is formed by four different cartilage- covered surfaces. The articulation is separated from 

 the posterior calcaneo-astragaloid joint by the sinus of the tarsus and its articular capsule exhibits 

 no special peculiarities. 



The calcaneocuboid articulation (Fig. 225) is the joint between the cuboid articular surface of 

 the calcaneus and the posterior articular surface of the cuboid bone. The surfaces are approxi- 

 mately saddle-shaped. Together with the talonavicular joint, it forms the transverse articulation 

 0] the tarsus (Chopart's joint). 



From a functional standpoint the talocalcaneo-navicular joint is composed of two portions. The first of these 

 is the joint between the talus (astragalus) and the navicular bone, which acts together with the calcaneo-cuboid articula- 

 tion. It is an ellipsoidal joint, while the talonavicular articulation is a saddle-joint. Although these joints are biaxial, 

 they check each other reciprocally, so that during motion each joint loses one of its axes of movement and a common 

 uniaxial hinge joint results, the transverse tarsal joint. The remaining portion of the talocalcaneo-navicular joint acts 

 together with the talocalcaneal joint, whose axis coincides with that of the transverse tarsal joint. Both joints, or rather 

 both combinations of joints, always work together; during adduction there is also an elevation of the inner margin of 

 the sole of the foot (supination), and during abduction there is a simultaneous elevation of the outer margin of the sole 

 of the foot (pronation). The anatomical and physiological associations of the joints are altogether different, as is also 

 the case at the elbow and at the inferior radio-ulnar articulation (see pages 122 and 123). 



The arthrodia of the tarsus consist of a variable number of single or combined articulations, 

 since neighboring articular cavities frequently intercommunicate, and while the number of articular 

 facets is relatively large, the number of joints is comparatively small because the small lateral 

 articular facets do not all form independent articulations. 



The cuneonavicular articulation (Fig. 225) is the joint between the articular surface of the 

 navicular bone and the posterior articular facets of the three cuneiform bones; it also extends 

 between the opposed articular facets of the cuneiform bones and between the internal articular 



