This is the largest bone in the hock. It is placed in front of the calcis, and from it project forward two pulley-like ridges separated by a deep groove. These ridges are received into two corresponding grooves already referred to as existing on the inferior extremity of the tibia, and the central ridge on the last-named part fits into the groove separating those on the astragalus. Together these two bones form the true hock joint, to which the movements of flexion and extension of the limb are for the most part due. The astragalus rests upon the cuneiform magnum, with which it forms a flattened gliding-joint of very limited movement. Behind, it articulates with the calcis.

Tibia (Posterior Aspect).

Fig. 311. - Tibia (Posterior Aspect).

1 Spine of Tibia. - Articulation of Fibula. 3 Fibula. 4 External Malleolus. 5 Internal Malleolus. 6 Shaft showing Bony Ridges for Muscular Attachment.