THE METATARSUS 123 
articulation with the fourth tarsal. In some cases there is a facet for the medial 
small metatarsal bone. 
THE FOURTH TARSAL BONE 
The fourth tarsal bone (Os tarsale quartum)' is the lateral bone of the distal 
row, and is equal in height to the central and third together. It is cuboid in shape 
and presents six surfaces. 
The proximal surface is convex from side to side, and articulates chiefly 
with the fibular tarsal, but to a small extent with the tibial tarsal also. 
The distal surface rests on the large and lateral 
small metatarsal bones. The medial surface bears 
four facets for articulation with the central and 
third tarsal bones. It is crossed from before back- 
ward by a smooth groove, which by apposition with 
the adjacent bones forms the canal of the tarsus (Can- 
alis tarsi) for the passage of the perforating tarsal 
vessels. The dorsal, lateral, and plantar surfaces are 
continuous and rough. A tuberosity behind gives 
attachment to the plantar igament. 
Development.—The fibular tarsal bone has two 
centers of ossification, one for the main mass and the 
other for the tuber calcis; the latter fuses with the rest 
of the bone at about three years of age. The first and 
second tarsals have separate centers, but fusion usu- 
ally occurs before birth. Each of the other bones 
ossifies from a single center. 
THE METATARSUS 
The metatarsal bones (Ossa metatarsalia), three 
in number, have the same general arrangement as 
Mt.If Mt. TIT Mt. 1V 
Fic. 112—Ricut Meratarsat Bones Fic. 113.—Proximiat Extremities oF Rigor Meratarsat Bones oF 
or Horse; Puiantar View. Horse; Env View. 
1, Rough area for attachment of 1, Facet for first tarsal; 2, 2’, facets for second tarsal; 3, 3’, facets for 
Suspensory ligament; 2, nutrient fora- third tarsal; 4, 4’, 4”, facets for fourth tarsal; 5, non-articular depression. 
men. Compare with Fig. 76. Compare with Fig. 77. 
the metacarpal bones, but present some important differences. Their direction is 
slightly oblique, downward, and a little forward. 
The third or large metatarsal bene (Os metatarsale tertium) is about one- 
sixth longer than the corresponding metacarpal; in an animal of medium size the 
1 Also termed the cuboid. 
