THE HIND EXTREMITIES. 95 



2. The lever bone. 



3. The buffer bones. 



The gliding bone is called the astragalus, and is 

 a large cubical block which carries the two large 

 gliding surfaces, on which glides the small end 

 of the tibia. These two large gliding surfaces have 

 a screw-like form which causes the parts be- 

 low the hock, when the toe is lifted, to move out- 

 wards. Then again this gliding surface is almost 

 parallel with the long axis of the hock and parts 

 below. Then again, and this is very important to 

 remember, when the foot is on the ground, the leg 

 at its straightest, and the very small end of the tibia 

 resting upon the top of this large gliding surface the 

 hock appears large, but when the leg is lifted, and 

 the small end of the tibia slides necessarily to the 

 bottom of this large gliding surface, the hock looks 

 small, therefore it is the relation of this large glid- 

 ing surface to the small surface at the lower end of 

 the tibia which determines the apparent size of the 

 hock. It follows that a bent hock which appears 

 smaller may he as large as a straight hock ivhich 

 appears larger. 



The lever bone or ' calcaneum,' is placed at the 

 top of the hock at the back, and is a lever of 

 the second order. The end of the long arm of this 

 lever is called the point of the hock, and corresponds 

 with our heel. It has attached to it the tendon 

 (called ' Tendo Achilles') of the large muscle whose 

 belly forms the so called calf of our leg. All de- 



