96 THE EXTERIOR OF THE HORSE. 



to place tlie organs of which it is the seat in the best conditions to 

 establish their proper relation with the external world. The most 

 interesting movements for us to study, however, are those whose object 

 is to modify the position of the centre of gravity while standing or 

 walking. The head occupies, in fact, at the anterior part of the trunk, 

 a position which also allows it to oscillate like a veritable pendulum at 

 the extremity of the cervical stalk. It may be raised or lowered, 

 remain in the axis of the body, or be displaced laterally, backward, or 

 forward ; in a word, the centre of gravity can be moved upward, 

 downward, forward, backward, sideways, raised from the base of sup- 

 port or drawn to it, removed from the centre of this base, forced out 

 of it, or again drawn back. These multiple actions are ])roduced still 

 more freely by the head when it is attached to a long neck, in which 

 case its movements are easier and more extended. Therefore, all the 

 influence which it exercises upon locomotion can be understood, since it 

 can, according to the will of the animal, change rapidly the condi- 

 tions of stability or instability of the equilibrium ; in a word, modify 



the speed. 



Not only do we speak of its extensive displacements, the effect of 

 which is understood at first sight, but we also make allusion to its 

 partial movements upon the neck. 



According to our researches, the centre of gravity of the head is 

 situated on the median line, at the intersection of a transversal plane, 

 which passes posterior to the last superior molar tooth, and of a hori- 

 zontal plane tangent to the palatine arch. Should the head be extended, 

 it becomes a mass of al)out fifteen to sixteen kilogrammes, which will 

 carry it, from this fact alone, in advance of the cervical lever, and 

 which will tend to deviate the line of gravitation in front of the base 

 of support. This is the attitude which it assumes in the race-horse 

 when he is running at full speed. When it becomes flexed, reverse 

 effects are produced ; when it is directed to the side, the corresponding 

 anterior member will at (Mice be overburdened, and the other as much 

 disburdened. This is sufficient to explain the importance of these total 

 and partial displacements. We will, besides, have occasion to return 

 to the subject when describing, in their proper place, the gaits, the 

 attitudes, and the movements which the animal performs. 



H. — Expression of the Head. 



The face of the horse is certainly the part of the body upon which 

 the sensations and tlie passions which ixe experiences show themselves 



