422 



HUMAN ANATOMY. 



the greater articular facet for the astragalus and a system of loops connecting them. 

 The large spaces are at the neutral point. 



Fig. 433. 



Longitudinal section of calcaneum, showing arrangement of lamellae. 



Development.— The chief nucleus is said to appear in the sixth month of 

 foetal life. We have twice seen it earlier, — once at about the fourth month. An 

 epiphysis for the back of the bone and the posterior plantar tubercles appears from 

 the seventh to the tenth year. It begins to fuse by fifteen, completing the process 

 in a year or so. 



THE CUBOID. 



The cuboid ' is a six-sided bone, flattened from above downward, interposed 

 between the calcaneum and the fourth and fifth metatarsal bones. It is important 

 to remember that the dorsal surface faces almost as much outward as it does upward. 

 The dorsal surface, slightly rough, has the following outline : an oblique posterior 

 dorder SLgSLinst the calcaneum, which, though most often convex, may be concave, 

 sinuous, or straight ; a short 02ifer concave one ; an internal one, at first straight 

 when against the scaphoid, and slanting outward when against the external cunei- 

 form ; and an anterior one, slanting outward and backward. The plantar surface 



Fig. 434. 



External cuneiform 



Fourth 

 meta- 

 tarsal 



Calcaneum 



Calcaneum 



Fifth 

 meta- 

 tarsal 



Groove 



Promontory For inf. calcaneo-cuboid ligament Promontory 



Right cuboid. A^ inner aspect ; B, posterior, outer, and inferior surfaces. 



has essentially the same shape, only the angle between the posterior and inner 

 borders is drawn out. Owing to the oblique position of the bone, this fits into the 

 upper inner angle of the anterior surface of the calcaneum. Just below this angle is 

 a prominence, the plantar t2ibcrcle. A thick, rounded, oblique ridge, the promon- 

 tory or tuberosity, starting at the back of the outer border, runs forward and inward 

 across the bone behind a groove between it and the anterior border. The tendon of 

 the peroneus longus lies on the smooth anterior slope of the promontory, the outer 



' Os cuboideum 



