524 COMPARATIVE PHYSIOLOGY. 



THE MUSCULAR SEiNSIi. 



Every one must be aware how difficult it is to regulate his 

 movements when the limbs are cold or otherwise deadened in 

 sensibility. We know too that, in judging of the muscular 

 effort necessary to be put forth to accomplish a feat, as throw- 

 ing a ball or lifting a weight, we judge by our past experience. 

 It is ludicrous to witness the failure of an individual to pick up 

 a mass of metal which was mistaken for wood. In these facts 

 we recognize that in the successful use of the muscles we are 

 dependent, not alone on the sensations derived from the skin, 

 but also from the muscles themselves. True, the muscles are 

 not very sensitive to pain when cut; it does not, however, fol- 

 low that they may not be sensitive to that different effect, their 

 own contraction. Whether the numerous Pacinian bodies 

 around joints, or the end-organs of the nerves of muscles are 

 directly concerned, is not determined. 



Pathological. — The teaching of disease is plainly indicative 

 of the importance of sensations derived both from the skin and 

 the muscles for co-ordination of muscular movements. 



In locomotor ataxy, in which the power of muscular co- 

 ordination is lost to a large extent, the lesions are in the pos- 

 terior columns of the spinal cord, or the posterior roots of the 

 nerves, or both, and these are the parts involved in the trans- 

 mission of afferent impulses. 



Comparative. — The more closely the higher vertebrates are 

 observed, the more convinced does one become that those sen- 

 sory judgments, based upon the information derived from the 

 skin and muscles, which they are constantly called upon to form 

 are in extent, variety, and perfection scarcely if at all surpassed 

 by those of man. Of course, sensory data in man, with his ex- 

 cessive cerebral development, may by associations in his expe- 

 rience be worked up into elaborate judgments impossible to the 

 brutes, but we now refer to the judgments of sense in them- 

 selves. 



The lips, the ears, the vibrissse or stiff hairs, especially about 

 the lips, the nose, in some cases the paws, all afford delicate and 

 extensive sensory data. 



It is a remarkable fact that the most intelligent of the 

 groups of animals have these sensory surfaces well developed, 

 as witness the elephant with his wonderful trunk, the hand of 

 the monkey, and the paws and vibrissas of the cat and dog tribe. 



