MECHANISM OF THE FETLOCK JOINT. 73 



Action of the Head and Neck in Locomotion. — During 

 movement, the head and neck act as a balancing pole in changing the 

 position of the centre of gravity from one side to the other, and in raising 

 or depressing it. Certain muscles of the neck draw the fore limb forward 

 and upward ; other muscles of the neck straighten out the head and neck, 

 and a third group bend them. 



Mechanism of the Fetlock Joint. — As Lecoq explains, " the 

 weight of the body, transmitted by the cannon-bone upon the upper 

 articulating surface of the long pastern bone, is the resistance to be 

 overcome. The fulcrum is the ground at the toe of the foot, and the 

 power acts upon the sesamoid bones, which are at the back of the pastern ; 

 the shortening of the flexor muscles being the cause of the straightening 



F ""^ w 



Fig. 45. — Mechanism of 

 Fetlock Joint. 



of the angle formed by their tendons." The diagram given in Fig. 45 

 will show how this lever (one of the second order) acts. In it we see 

 that the distance between the power and weight remains constant ; but 

 their respective distances from the fulcrum vary according to the slope 

 of the pastern and hoof, and according to the length from the fetlock 

 to the toe. Hence (pp. 56 to 58), the shorter is the distance of the toe 

 from the direction of the cannon-bone, or from that of the back-tendons, 

 the greater will be the mechanical advantage at which the back-tendons 

 will act ; and vice versa. On the other hand, we may see that the more 

 is the mechanical gain, the worse will the fetlock act as a spring, which 

 function is all important in saving the hmb (especially the fore one) 

 from the injurious effects of concussion. It is evident that the distance 

 of the weight (or power) from the fulcrum (F) is influenced by the length 

 and slope of the pastern ; it being greatest when the pastern is long 

 and obhque, and least when that part is short and upright. Also, 

 increased growth of hoof, either at the toe or heel, will affect the slope 

 in question, and the thickness of horn at the toe will, of course, influ- 

 ence the length from the fetlock to the toe. As a practical point, we 



