2S8 A MANUAL OF ANATOMY 



the outer head of the abductor hallucis, the flexor brevis digitorum, 

 and a portion of the abductor minimi digiti. The greater part of 

 the inferior surface gives attachment to the long plantar ligament, 

 and anteriorly it presents a small round eminence, called the anterior 

 tubercle, to which the short plantar ligament is attached. 



The internal surface is concave, and is overhung at -its antero- 

 superior part by the sustentaculum tali. This latter is concave 

 and articular above for the astragalus, and below it presents a groove 

 for the flexor longus hallucis. Anteriorly it gives attachment to the 

 inferior calcaneo-navicular or ' spring ' ligament, below which a slip 

 of the tibialis posticus takes insertion, and its inner margin gives 

 attachment to fibres of the internal lateral ligament of the ankle- 

 joint. The general concavity of the internal surface supports the 

 tendon of the flexor longus digitorum and the plantar vessels and 

 nerves, and anteriorly it affords origin to the inner head of the 

 flexor accessorius. 



The external surface is for the most part fiat. Towards its 

 anterior and lower part it presents a short oblique ridge, called the 

 peroneal spine or ridge, which separates two grooves. The upper 

 groove transmits the tendon of the peroneus brevis, and the lower 

 that of the peroneus longus. Behind and a little above this spine 

 there is a small tubercle, about the centre of the surface, for the 

 middle fasciculus of the external lateral ligament of the ankle-joint. 



The OS calcis is pierced by many nutrient foramina for offsets 

 of the calcaneal branches of the posterior tibial and external 

 plantar, and the internal and external malleolar branches of the 

 anterior tibial, arteries. 



Articulations. — Superiorly with the astragalus, and anteriorly 

 with the cuboid. 



Structure.— rThe structure is that of a short bone. Some of the 

 lamellae of the cancellated tissue arch downwards and backwards 

 from the large postero-external facet on the superior surface to the 

 prominence of the heel. In addition to these, there are other 

 lamellae which pass in an antero-posterior direction just above the 

 layer of compact bone which forms the plantar surface. In the 

 region of the groove for the sinus pedis, especially towards the outer 

 part, the upper compact layer is thicker than elsewhere. 



Ossification. — The os calcis ossifies in cartilage from one primary, and one 

 secondary, centre. The primary centre appears in the sixth month of intra- 

 uterine life. The secondary centre appears in the tenth year, and forms a 

 thin epiphysial scale over the posterior surface of tfie tuber calcis, wliich joins 

 in the sixteenth year. This epiphysis includes the outer, and a large part of 

 the inner, tubercle on the under surface, and it may include the whole of the 

 posterior surface, or only the lower two-thirds. 



The Navicular Bone. 



The navicular or scaphoid bone is distinguished by its resemblance 

 to a boat. It is situated on the inner side of the foot, where it is 

 placed in front of the astragalus, and behind the three cuneiform 



