42 SCIENTIFIC HORSESHOEING. 



animal oil that facilitates the gliding of the articular surfaces 

 and tendons. It is the vital lubricant of the living machine, and 

 its use in the animal economy is identical with that of other 

 greasy substances employed to lubricate mechanical bearings. 

 See colored plates. 



Muscles of the Foot and Leg. — Following the indication 

 given of the passive organs of locomotion, the bony levers and 

 their joints, comes a reference to the active agents whose func- 

 tion it is to move them. These are the muscles, and form, gen- 

 erally speaking, the fleshy covering surrounding ilie bony 

 frame-work and grouped around and attached to the bones of 

 the extremities. 



The situation and direction of the muscles are important 

 features to be acquired with regard to their arrangement and 

 use in communicating motion to the leg and foot, for it allows 

 the determination of the angle of incidence of a muscle on its 

 arm of the lever, the relation of its principal axis to the vertical 

 line, and its comparison with the axis of the bony lever which it 

 moves. If the direction of the muscles be compared with that 

 of the bones of the limb that they move, it will be found that 

 they are parallel to these levers, and the proper direction of the 

 bones being known to be rectilinear, that is, their principal axis 

 being straight or parallel to the median plane of the body, it is 

 sufficient to indicate that of the muscles to clearly establish this 

 comparison. Undoubtedly the most essential part of the study 

 of the muscles is their attachments or insertions, for with this 

 knowledge we may determine their extent and direction, and 

 even their relations and uses. The principal muscles of the 

 extremities have fixed insertions of a cordy structure known as 

 tendon or sinew. The superficial muscles are only related to 

 the bones by their extremities, while the deep muscles are ap- 

 plied by their bodies directly against the bones of the skeleton. 

 Three principal tendons serve to move the bones of the foot. 



