572 A MANUAL OF VETERINARY PHYSIOLOGY 



municated to the cerebrum, from which impulses pass from the 

 centre representing the muscles to the muscles themselves. It 

 would appear that centres must exist in the cord by which at 

 least part of this work is carried out, for it has been shown 

 (p. 449) that after it has been divided in the dog, and sufficient 

 time has elapsed, muscular co-ordination is re-established, 

 though no communication with the brain is possible. There 

 are other reasons which have also been mentioned which suggest 

 that the cord of the lower animals is capable of automatic 

 activity in the matter of muscular movements, being stimulated 

 by the constant inpouring of sensory impulses through the 

 muscle-aff eren ts . 



Deep pressure sensibility, such as arises from joints, and the 

 sensory impressions arising in the skin and subcutaneous tissues 

 of joints, are intimately concerned in the kinaesthetic sense. It 

 is probable that it is particularly in operation in determining 

 weight and resistance, and it would appear to be well developed 

 in draught-horses. The horse employed in ' shunting ' knows in 

 a second the amount of effort required to start truck-loads of 

 varying weight. This information is transmitted through the 

 skin under the collar and over the large joints, especially 

 the shoulder, hip, and stifle. 



The importance of * muscle sense ' in provoking a muscular 

 contraction is shown by the pseudo-paralysis which follows 

 division of the sensory nerves. This operation causes no loss of 

 power, but it cuts off all afferent impressions from the muscles 

 of the part ; the dog drags his legs, the arm of the monkey hangs 

 helplessly, in spite of the fact that in neither case have the motor 

 mechanisms been interfered with. The same is seen in the horse 

 on dividing the superior maxillary branch of the fifth nerve ; the 

 animal is unable to use his lips as a prehensile organ, though 

 they possess their full share of power. 



Judgment of distance, the relationship of space, and the 

 muscular co-ordination connected with equilibrium, are in- 

 definably mixed up with muscle-sense, vision, and the internal 

 ear. The extraordinary judgment shown by horses in jumping, 

 both as to height and distance, is mediated through this 

 channel. Some animals never acquire it, are clumsy, make but 

 little effort to rise, or, if tired, none whatever ; others are willing, 

 but their judgment is defective, and the muscles are directed to 

 perform unnecessarily powerful contractions ; a third group, 

 confident in their powers and judgment, and unwilling to do 

 more than is necessary, run matters so fine that it requires a fall 

 to remove their pride. Muscle-sensation is very evident in the 

 tired animal, and is probably the only occasion, apart from 

 lameness, in which a horse is conscious of possessing limbs. 



