THE HOCK JOINT 121 



The Nerves 



The external saphena nerve runs down the outer aspect of the limb 

 in front of the tendo-achilles, occupying a position on this side of the limb 

 corresponding to that in which the posterior tibial nerve is found on the 

 inner aspect. It crosses the postero-external aspect of the hock, being 

 very superficially placed. Similarly placed in a superficial position, we 

 find, on the anterior and antero-external aspects of the joint, two (some- 

 times three) terminal divisions of the musculo-cutaneous nerve. The 

 anterior tibial nerve is more deeply seated and passes over the front of the 

 tarsus. Below the hock it follows the course of the large metatarsal 

 artery. It gives filaments to the tarsus. The posterior tibial nerve descends 

 the inner aspect of the limb in front of the tendo-achilles. About five 

 inches above the point of the hock it gives off a small filament which 

 runs obliquely downwards, forwards and inwards over the antero-internal 

 aspect of the joint. It is a cutaneous branch. The posterior tibial nerve 

 then divides into the external and internal plantar nerves, which run 

 through the tarsal sheath one on either edge of the perforans tendon. 

 Articular branches are also contributed by this nerve. Tiny branches of 

 the internal saphena nerve may be found on the front and internal aspect 

 of the joint. They are very superficially placed, and in many cases do not 

 extend as far as the joint. 



Movements of the ^Joints of the Tarsus. — Although the hock is of such 

 complicated structure its movements are very simple. The only joint 

 which is of any importance so far as movement is concerned is that 

 formed between the tibia and astragalus, and in this joint the move- 

 ments are restricted to simple flexion and extension. It is a typical 

 member of the class ot ginglymoid joints. Lateral movement is com- 

 pletely restricted on account of the conformation of the articular 

 surfaces and the disposition of the lateral ligaments. When the animal 

 stands with both hind feet in line and resting flat on the ground, the 



