102 ATLAS AND TEXT-BOOK OF HUMAN ANATOMY. 



Fig. 153. — A frozen preparation of the bones of the foot seen from the plantar surface (|). 



Fig. 154. — The same preparation seen from the dorsal surface (f). 



Fig. 155. — The same preparation seen from the outer side (f). 



Fig. 156. — The right talus (astragalus) seen from below (f). 



Fig. 157. — The right talus (astragalus) seen from above (f). 



THE TARSAL BONES. 

 The tarsus (Figs. 153 to 155) consists of seven bones. (1) The talus or astragalus; (2) the 

 calcaneus; (3) the navicular or scaphoid bone; (4) the cuboid bone; and (5 to 7) the external, 

 middle, and internal cuneiform bones. Only in the distal portion of the tarsus, where the cuboid 

 articulates with the three cuneiform bones, is there an indication of an arrangement in rows as in 

 the carpus, and in further contrast to the hand, a single tarsal bone articulates with both bones 

 of the leg, while the carpus articulates with the radius only. 



THE TALUS. 



The talus or ast ragalus (Figs. 156, 157) is a short bone, irregularly cuboid in shape, and is 

 composed "oTabody and of a head, the constriction between the two being termed the neck. 



The body is the thickest and most posterior portion of the bone. Its upper surface presents 

 a cartilaginous trochlear surface, the trochlea (Fig. 157), with which the tibia and fibula articulate, 

 and it possesses three surfaces, a large superior one and two smaller lateral ones. The superior 

 surface is convex in the longitudinal (sagittal) axis of the bone and concave from side to side; it 

 is broad anteriorly and narrow posteriorly. The lateral surfaces are almost flat and approxi- 

 mately triangular, the external one being much larger than the internal. The external surface 

 is known as the external malleolar surface; it forms the outer side of the astragalus and is con- 

 tinued upon a strong process of the bone, the external process (Figs. 154 and 156), which is 

 directed outward. The internal surface forms a part of the inner side of the astragalus, the 

 remainder of which is rough, and is termed the internal malleolar surface. Behind the trochlea 

 and directed backward is the posterior process (Fig. 157), which is notched by a broad groove 

 for the tendon of the flexor hallucis longus.* The lower surface of the bone (Fig. 156) presents 

 a distinctly concave, almost transverse, ovoid articular facet, the posterior articular facet, for the 

 calcaneus, whose outer portion lies upon the lower surface of the external process, while its inner 

 and posterior portion is upon the corresponding surface of the posterior process. 



In front of this articular facet is situated a broad groove, the sulcus tali (Fig. 155), which is 

 wider externally than internally and the floor of which is roughened. Together with the similar 

 groove of the calcaneus it forms the sinus of the tarsus, which is filled by ligaments. 



In the region of the neck the lower surface of the astragalus in front of the sulcus tali presents 

 an oblong, slightly convex, articular facet, parallel to the posterior one, and known as the 

 middle articular facet for the calcaneus, and bordering upon this, and forming a portion of the head 

 of the talus, is a small, slightly convex elliptical anterior articular facet for the calcaneus 

 (Fig. 156). 



* There may consequently be distinguished upon the posterior process an internal and an external tubercle. 



