120 THE SKELETON OF THE HORSE 
THE TIBIAL TARSAL BONE 
The tibial tarsal bone (Os tarsi tibiale)! is the medial bone of the proximal row. 
It is extremely irregular in form, but may be considered as offering six surfaces for 
description. 
The proximal and dorsal surfaces are continuous, and form a trochlea (‘Troch- 
lea tali) for articulation with the distal end of the tibia. The trochlea consists 
of two oblique ridges with a deep groove 
between them; these curve spirally for- 
ward, downward, and outward, forming 
an angle of 12 to 15 degrees with a sagittal 
plane. There is usually a shallow synovial 
fossa in the groove. The distal surface is 
convex from before backward. and most 
of it articulates with the central tarsal; 
laterally it has an oblique facet for the 
fourth tarsal, and a non-articular groove 
cuts into the surface to its middle. The 
plantar surface (Facies plantaris) is ob- 
lique and extremely irregular; it presents 
four facets for articulation with the fibular 
tarsal bone; the facets are separated by 
Trochlea 
Fic. 105.—Ricur Tarsus anp ProximMaL Parr oF Fic. 106.—Ricur Tristar Tarsat Bone or Horse; PLan- 
Meratarsvus oF Horse; LaTeraut VIEW. TAR VIEW. 
Tt, Tibial tarsal (trochlea); Ty, fibular tarsal 1-4, Facets for articulation with fibular tarsal; 5, fossa; 
(body); Tc, central tarsal; T3, third tarsal; T4, 6, distal tuberosity; 7, proximal tuberosity. 
fourth tarsal; 1, depression for attachment of lateral 
2 3, prominence for 
ligament; 2, processus cochlear 
atacment of trl Henment: 4 erm fF #*t ough excavated areas, and the largest 
tarsal bones. Arrow points to vascular canal. fossa (Sulcus tali) forms with a corres- 
ponding one on the fibular tarsal a cavity 
termed the sinus tarsi. The medial surface bears on its distal part a large tuber- 
osity and on its proximal part a small one for the attachment of the medial liga- 
ment of the hock joint. The lateral surface is smaller than the medial, and is 
marked by a wide rough fossa in which the lateral ligament is attached. 
THE FIBULAR TARSAL BONE 
The fibular tarsal bone (Os tarsi fibulare)? is the largest bone of the hock. It 
is elongated, flattened from side to side, and forms a lever for the muscles which 
1 Also termed the astragalus or talus. 2 Also termed the caleaneum or os calcis. 
