THE METATARSUS 



123 



articulation with the fourth tarsal, 

 small metatarsal bone. 



In some cases there is a facet for the medial 



The Fourth Tarsal Bone 

 The fourth tarsal bone (Os tarsale quartum)i 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 ligament. 



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. II Mt. Ill 



ML IV 



Fig. 112, — Right Metatarsal Bones 

 OF Horse; Plantar View. 

 1, Rough area for attachment of 

 suspensory ligament; 2, nutrient fora- 

 men. Compare with Fig. 76. 



Fig. 113. — Proximal Extremities of Right ^Metatarsal Bones of 

 Horse; End View. 



1, Facet for first tarsal; 2, 2', facets for second tarsal; 3, 3', facets for 

 third tarsal; 4, 4', 4", facets for fourth tarsal; 5, non-articular depression. 

 Compare with Fig. 77. 



the metacarpal boneSj but present some important differences. Their direction is 

 shghtly oblique, downward, and a little forward. 



The third or large metatarsal bone (Os metatarsale tertium) is about one- 

 sixth longer than the corresponding metacarpal; in an animal of medium size the 



^ Also termed the cuboid. 



