202 THE EXTERIOR OF THE HORSE. 



forms the summit of the scapulo-humeral angle and indicates externally 

 the origin of the region of the arm ; finally, immediately behind this 

 angle, and upon the external surface of the great extensor of the fore- 

 arm, is found what is termed the blemish of the shoulder. An ordinance 

 of sanitary police, of the 31st of August, 1842, prescribed that all 

 horses suspected of suffering from contagious diseases should be marked 

 in this region by a square brand. 



In fat and well-muscled horses these prominences of the shoulder 

 are almost completely effaced ; the external face, the anterior border, 

 and the articulation become rounded and insensibly confounded with 

 the adjoining regions; the form of the shoulder must be surmised 

 rather than perceived, unless it is revealed while the animal is exer- 

 cised at a more or less rapid gait, in which event its movements will 

 inform us as to its general form, its dimensions, and its direction. 



Movements. — When, during the walk, the anterior member 

 leaves its point of contact with the ground, it becomes shortened, 

 directed forward, and all the articular angles close themselves by the 

 flexion of the segments which form them, and the foot is elevated a 

 certain distance above the soil. But if the shortening were manifested 

 only in a vertical direction, it is easy to understand that the foot 

 would arrive at precisely the same point which it previously occupied 

 without, of course, communicating any propulsion to the trunk. 



In order to give amplitude ^ to the step, it is indispensable there- 

 fore that the bones be carried forward, and that the displacements 

 begin at the superior extremity of the limb (the scapula) and terminate 

 with the foot, one piece being moved upon the other. 



The shoulder is the region whence proceed the initial movements 

 when the member is advanced. 



In this phenomenon the shoulder is slightly elevated by means of 

 the surrounding muscles ; its humeral angle rotates forward while its 

 superior border is carried downward and backward, and the extent of 

 this movement is directly proportional to the length of the muscles 

 which produce it. 



The elevation of the humeral angle is effected principally, through its con- 

 nection with the humerus, by the strong mastoido-humeralis muscle which ex= 

 pands over the anterior surface of the articulation. It is aided in this action by 



1 We designate under this name the linear displacement of the inferior extremity of the 

 member in advance of its vertical axis, the result of the successive movements of the angles and 

 bones which compose it. This displacement is equal to one-half of the oscillation of the motor 

 column, which is, metaphorically speaking, not unlike a body swinging to and fro in the man- 

 ner of an articulated pendulum, but with this difference, that here the muscular contraction 

 replaces the weight which alone causes the latter to oscillate. 



