The =central tarsal= bone (Os tarsi centrale, scaphoid, or navicular) is
irregularly quadrilateral, and is situated between the tibial tarsal
above and the third tarsal below. It is flattened from above downward,
and may be described as having two surfaces and four borders. The
=superior surface= is concave from before backward, and almost all of it
articulates with the tibial tarsal; a non-articular depression cuts into
its outer part, and sometimes there is a facet for the fibular tarsal
bone on the posterior angle. The =inferior 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 =anterior= or =dorsal border= and the =internal border= are
continuous, convex, and rough. The =posterior= or =plantar border= bears
two prominences, separated by a notch. The =external border= is oblique,
and bears anterior and posterior facets for articulation with the fourth
tarsal, between which it is excavated and rough.
[Illustration:
FIG. 84.—RIGHT TARSAL AND METATARSAL BONES OF HORSE. EXTERNAL VIEW.
(After Schmaltz, Atlas d. d. Anat. d. Pferdes.)
]