THE CENTRAL TARSAL BONE 121 
extend the hock joint. It consists of a body and a medial process, the sustentacu- 
lum tali. 
The body (Corpus) is enlarged at its proximal end to form the tuber calcis or 
“Hoint of the hock’’; the posterior part of this eminence gives attachment to the 
tendon of the gastrocnemius, while in front and on each side it furnishes insertion 
to tendons of the superficial digital flexor, biceps, and semitendinosus muscles. 
The distal extremity bears a concave facet for articulation with the fourth tarsal 
bone. The medial surface of the body has on its lower part a strong process, the 
sustentaculum tali, which projects inward. The process has a large, oval, slightly 
concave facet in front for articulation with the tibial tarsal, and sometimes a small 
articular surface below for the central bone. Its plantar surface forms with the 
smooth medial surface of the body a groove for the deep flexor tendon (Sulcus tarsi). 
Its medial surface has a prominence on the distal part for the attachment of the 
medial ligament. The lateral surface of the body is flattened, except below, where 
there is a rough prominence for the attachment of the lateral 
ligament. The dorsal border is concave inits length, smooth 
Tuber and rounded in its upper part. About its middle is a blunt- 
ealeis — nointed projection (Processus cochlearis) which bears facets 
on its medial and lower surfaces for articulation with the 
tibial tarsal bone, and is roughened laterally for ligamen- 
tous attachment. Below this are two facets for the tibial 
tarsal, and an extensive rough fossa which concurs in 
the formation of the sinus tarsi. The plantar border is 
Susten- straight and broad, and widens a little at each end; it is 
taculum rough, and gives attachment to the long plantar ligament. 
Fic. 107.—Ricur Frsvrar Fic. 108.—Ricur Centrat Tarsat Bone or Horse; PRoxIMAL SURFACE. 
TarsaL Bone or Horse; 
Dorsat Visw. 
1, Articular surface for tibial tarsal; 2, facet for fibular tarsal; 3, non-articular 
depression. 
1+, Facets for articulation with 
tibial tarsal bone; 5, fossa. 
THE CENTRAL TARSAL BONE 
The central tarsal bone (Os tarsi centrale)! is irregularly quadrilateral, and is 
situated between the tibial tarsal and the third tarsal. It is flattened from above 
downward, and may be described as having two surfaces and four borders. The 
proximal surface is concave from before backward, and almost all of it articulates 
with the tibial tarsal; a non-articular depression cuts into its lateral part, and 
sometimes there is a facet for the fibular tarsal bone on the posterior angle. The 
distal surface is convex, and is crossed by a non-articular groove, which separates 
facets for articulation with the third and the first and second (fused) tarsals. The 
dorsal border and the medial border are continuous, convex, and rough. The 
plantar border bears two prominences, separated by a notch. The lateral border 
is oblique, and bears anterior and posterior facets for articulation with the fourth 
tarsal, between which it is excavated and rough. 
1 Also termed the scaphoid or nayicular bone. 
