THE OS CALCIS. 237 
spring the fibres of origin of the abductor minimi digiti muscle. On the fore-part 
of the under surface there is an elevated elongated tubercle, which terminates 
somewhat abruptly just behind the anterior border of this aspect of the bone, 
giving rise at times to a notch. From the former spring the fibres of the long 
plantar ligament, whilst the latter serves for the attachment of the deeper fibres of 
the short plantar ligament. The two heads of origin of the flexor accessorius 
muscle arise from the bone on either side of the long plantar ligament. The 
internal surface of the os calcis is crossed obliquely from above downwards and 
forwards by a broad groove of considerable depth; along this pass many of the 
structures which enter the sole of the foot from the back of the leg. The groove 
is overhung in front and above 
by a projecting bracket - like eR aT a 
process, called the sustentaculum — | sai cae ee 
tali, or lesser process. ‘The eh \ GROOVE 
under surface of the susten- X 
taculum is channelled by a 
groove, in which is lodged the 
tendon of the flexor longus 
hallucis muscle; whilst its inner 
border, to which is attached a 
part of the internal lateral 
ligament of the ankle, is over- 
lain by the tendon of the flexor 
FACETS FOR ASTRAGALUS 
CuBOID 
longus digitorum. To the 
anterior border of the susten- Oa GS EROLE 
taculum is attached the inferior A 
caleaneo - navicular ligament, A, As seen from the Outer Side. 
and placed on its upper surface 
is the articular facet already Be sibatee ey ase ce 
alluded to (facies articularis — . Ay". Mip. Post. 
media). Posteriorly the in- 
ternal surface of the bone is 
limited inferiorly by the pro- 
jection of the internal tubercle, 
and above by the internal 
lipped edge of the tuberosity. 
The external surface, broad 
behind and narrower in front, 
is of flattened form. Springing 
from it, just below the outer 
end of the sinus tarsi, 1S Susrenracunum GROOVE FOR 
CuRBOID 
TUBEROSITY 
the peroneal spine (processus ‘*” smears SS 
trochlearis), often indistinctly EXTERNAL TUBERCLE %JNTERNAL TUBERCLE 
marked. To this the fibres of B 
the external annular ligament B, As seen from the Inner Side. 
are attached; whilst in grooves 
above and below it pass the 
tendons of the peroneus brevis and longus muscles respectively. ‘To the upper 
and back part of this surface are attached the fibres of the middle fasciculus of the 
external lateral ligament of the ankle. 
The anterior extremity, sometimes called the greater process, is furnished with a 
saddle-shaped surface on its anterior aspect for articulation with the cuboid. This 
facet is concave from above downwards, and slightly convex from side to side; its 
edges are sharply defined, except internally, and serve for the attachment of 
ligaments. . 
The posterior extremity, called the tuberosity (tuber calcanei) forms the 
projection of the heel. Of oval form and rounded surface, it rests upon the two 
tubercles inferiorly. Its cutaneous aspect is divisible into three areas. Of these 
Fic, 179.—THE Ricur Os CaLcis. 
the highest is smooth and erescentic, and is covered by a bursa; the intermediate is 
