The navicular bone is a small flattened bone, broad in the middle and tapering towards each extremity. It is situated in the hoof, below the os corone and behind the os pedis, with both of which it articulates to form the coffin-joint. The great flexor tendon passes over its under surface, and between the two a synovial membrane exists to lubricate the surfaces of contact and facilitate movement. The anterior border articulates with the foot-bone, as already explained, and is connected below with the inferior navicular ligament. The posterior border affords attachment to the posterior navicular ligament. To the pointed extremities are attached lateral ligaments which unite the bone with the os pedis, the lateral cartilages, and the coronet bone.

The navicular bone is the seat of that very common ailment, navicular disease.

Fig. 307. - Os Pedis (Side View).

a Coronal Process. B Superior Border. c, D Basilar and Re-irossal Processes, forming one of the alae or wings. E Preplantar Fissure. F Facet for Insertion of the Extensor Pedis.