THE POSTERIOR LIMBS. 



145 



between the inferior extremity of the tibia and the superior extremity of the 

 metatarsal bones ; they are arranged, like the bones of the carpus, in two tiers — 

 a superior and an inferior. 



The superior row only comprises two bones, Fig. 98. 



the largest ; these are the astragalits and the 

 calcnneum (or calcifi). The inferior row is formed, 

 outwardly, of the cuboides alone ; inwardly and 

 anteriorly, it is subdivided into two secondary 

 rows, the superior of which is constituted by the 

 scaphoidcs, and the inferior by the laruc and small 

 cuneiform bones. The last is sometimes divided 

 into two, in which case there are three cunei- 

 forms ; then the total number of the bones is 

 seven. 



Astragalus. — An irregular cubical bone, situ- 

 ated in front of the calcis, between the tibia 

 and the scaphoid, and divided into five faces : 

 1. A supfriur and anterior, formed as an articular 

 pulley to correspond with the inferior extremity of 

 the tibia. This pulley — oblique from above down- 

 wards, forwards, and outwards — may be considered 

 as the type of the most perfect trochlea in the 

 body ; it forms with the median plane of the body 

 an angle of from 12° to 1.')°. Its borders are 

 slightly spiral, the inner being more prolonged 

 backwards than the external ; its groove receives 

 the median tenon of the tibia, and its two ridges 

 or lips fit into the lateral furrows of that bone ; 

 the two lips are deeply implanted in the lateral 

 grooves, and their two fossa? are hollowed out of 

 their lower extremity, to admit the end of the 

 principal bone during flexion movements. 2. An 

 infei-ior fare, occupied by a slightly convex articu- 

 lar surface articulating with the scaphoid ; this 

 surface is notched outwardly by an excavation for 

 ligamentous insertion ; behind the internal ex- 

 tremity of this furrow, the articular face is cut 

 in such a manner as to present two facets inclined 

 towards each other, and separated by a sharp 

 ridge. ?>. A posterior face, irregular, cut into three 

 or four diarthrodial facets adapted for similar 

 facets on the calcis, and which are separated by 

 a wide, rugged excavation ; the middle facet is 

 elliptical, almost vertical, slightly convex, and is 

 the largest. 4. An external face, covered with 

 imprints for the tibo-tarsal ligaments. 5. An 

 internal fare, provided below with a small tubercle 

 for insertion, and, posteriorly, with a badly defined 

 sinuous furrow for the tendon of the oblique flexor 

 muscle of the phalanges (Fig. 99). 



lfft hind poot (external 

 aspect). 



1, Tibia ; 2, summit of calcis or cal- 

 caneum ; 3, astragalus ; 4, cuboid; 

 5, scaphoid; 6, cuneiform mag- 

 num ; 7, large metatarsal bone ; 

 8, small metatarsal bone ; 9, suf- 

 fraginis, proximal, or first pha- 

 lanx ; 10, sesamoid bones; 11, 

 cor jnarv, second, or middle pha- 

 lanx ; 12, pedal bone, or third or 

 distal phalanx; 14, navicular 

 bone ; 15, basilar process of pedal 

 bone. 



