THE SKELETAL SYSTEM 47 



The distal extremity carries an articular surface composed of two 

 deep furrows with a ridge between for the tibial tarsal bone. 



The fibula is a reduced long bone situated along the outer 

 border of the tibia, with which it articulates at the proximal ex- 

 tremity. The distal extremity ends as bone about the lower third 

 of the tibia, but is continued by a fibrous cord to the distal end of 

 the tibia. 



The tarsus, or hock, is composed of a collection of short bones 

 situated between the tibia and the metatarsus (Fig. 5). There 

 are six or seven bones in the group, arranged in two rows, with a 

 central bone between. The upper row contains the tibial and 

 fibular tarsal bones, below which lies the central. The lower row is 

 made up of the fused first and second, third, and fourth tarsal 

 bones. ^ The fibular tarsal is the largest of the bones of the tarsus 

 and consists of a body which is provided with facets for articulation 

 with the adjoining bones. Projecting upward and backward from 

 the body is a prominence which corresponds to the heel of man. In 

 the horse it forms the point of the hock (tuber calcis). The tibial 

 tarsal is the inner bone of the upper row. Its superior and anterior 

 surfaces are continuous and present two ridges, with a furrow be- 

 tween, which are directed obliquely forward and outward for 

 articulation above with the distal end of the tibia. The central 

 tarsal is situated between the two rows. The first and second are 

 usually united to form a single bone. The third is somewhat like 

 the central in form and appearance. The fourth is cubical in 

 shape. 



The metatarsus is composed, like the corresponding region in 

 the fore limb, of the cannon and two splint bones. These bones are 

 directed downward and a little forward. The hind cannon is 

 about one-sixth longer than that of the fore limb; in a medium-sized 

 animal the difference is about 2 inches. On cross-section it is 

 more nearly circular in outhne. The spUnts are larger and stronger, 

 the external being relatively massive. 



The digit of the hind limb is similar to that of the fore. The 

 principal differential features lie in the third phalanx, which has a 

 less oblique wall, a narrower toe, and a sole surface that is more 

 concave. The distance between the angles or wings is less than in 

 the fore coffin bone. 



' These names apply when viewing the hock from the front and from within 

 outward. 



