754 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



cervical vertebrae. The pelvis and posterior part of the vertebral column 

 is raised, this elevation being assisted by and coinciding with the sudden 

 extension of the hind legs, the feet leaving the ground and being ex- 

 tended by the muscles of the upper joint of the leg, the lower joints 

 likewise being subsequently extended. Here, also, both fore feet are not 

 parallel on the ground, but one is somewhat advanced in front of the 

 other. The hind foot on the diagonal side is somewhat sooner raised, 

 and, therefore, further extended than the other (Fig. 311). In this act 

 the centre of gravity never nearly approaches the line of direction of the 

 fore legs, so that this position can be maintained but for an instant, the 

 trunk sinking again by its own weight, and is supported by the hind 

 legs, which are now flexed and drawn under the body. 



(c) Lying Down and Rising Up. The first stage of lying down in 

 the horse consists in the backward motion of the fore feet and the for- 

 ward motion of the hind feet, thus greatly reducing the base of support. 

 A sudden flexion of the fore legs then occurs, so that the animal falls on 

 its knees ; then the hind legs become flexed, so that the posterior surface 

 of the tibiae touches the ground. The act of lying down, therefore, in 

 the horse is practically falling down. While lying one side of the 

 body completely touches the ground, the limbs being extended from the 

 body either in slight flexion or in complete extension. In rising up the 

 extended extremities are drawn to the body, and by the unilateral action 

 of the trunk muscles the body is brought in such a position that the 

 chest and abdomen are in contact with the ground, the fore feet are then 

 extended on the ground, and a fixed point for the back muscles thus being 

 acquired, the contraction of these muscles draws the pelvis forward, so 

 that the hind legs are now enabled to bring the feet against the ground, 

 and by sudden extension of all the legs the bod}' is raised up. 



(d) Walking Backward. In walking backward in the horse the head 

 and neck are elevated, the spinal column, through the contraction of its 

 muscles, rendered rigid, and the fore legs in a somewhat flexed condition 

 are directed from above backward and downward, and then, in contact 

 with the ground, gradually extended, being assisted by the contraction 

 of the pectoralis major and latissimus dorsi, serve to push the body back- 

 ward from the flexed hind legs. The backward movement occurs by the 

 alternate movement of the diagonal feet ; thus, it may commence with 

 the fixation and extension of the right fore foot, then the left hind foot, 

 then the left fore foot, and then the right hind foot. The foot which is 

 raised up is, however, again placed on the ground and commences to act 

 as a supporting member before the foot which is next elevated has left 

 the ground. Consequently, support continues on three feet at one time, 

 and the period of support lasts much longer than that of forward move- 

 ment. Walking backward in quadrupeds is, therefore, an extremely slow 



