CUTANEOUS AND INTERNAL SENSATIONS. 269 



of equilibrium. Indeed, section of the posterior roots of the spinal 

 nerves supplying a given region is followed by a loss of control 

 of the muscles in this region hardly less complete than the paralysis 

 produced by direct section of the anterior roots; the muscles not 

 only lose their tonicity in consequence of the dropping out of the 

 reflex sensory stimuli from the skin and muscles of the region, but 

 they are apparently withdrawn from voluntary control in spite of 

 the maintenance of their normal motor connections. Within the 

 central nervous system the fibers of muscle sense end in part in 

 the cerebellum and in part ''pass forward, by way of the median 

 fillet, to end in the cerebrum. In the cerebrum they end in the 

 cortex of the parietal lobe in the region of the posterior central 

 convolution. There is reason to believe that this cortical sense 

 area of the muscle sense is connected by association fibers with 

 the motor areas lying anterior to the fissure of Rolando, and we 

 have thus a reflex arc, or, as Bell expressed it, a circle of nerves 

 between the muscles and the brain. It is probable that a similar 

 arc or circle is formed by the connections through the cerebellum, 

 and still a third one of a lower order by the connections in the 

 spinal cord. In the higher animals the impulses received in the 

 cerebellum through the fibers of muscle sense, in connection with 

 those received from the semicircular canals and vestibular sacs 

 of the ear, furnish the sensory basis for the cerebellar control of 

 muscular movements, particularly of the synergetic combination 

 necessary in locomotion. Through the circle or arc in the cortex 

 of the cerebrum it may be supposed that our characteristic volun- 

 tary movements are effected, and it may be doubted whether a 

 so-called voluntary contraction can be made when this circle is 

 broken on the sensory side. Whether or not this latter suggestion 

 is true it seems to be beyond doubt that adequately controlled 

 voluntary movements depend for their adaptation upon the 

 inflow of sensory impulses along the fibers of muscle sense. We 

 have a certain consciousness of the condition of our muscles at 

 all times, and if we were deprived of this knowledge we should be 

 unable to control them properly, perhaps unable to use them 

 voluntarily. 



The Quality of the Muscle Sense. Our conscious realization 

 of muscular sensibility is not distinct. Under ordinary conditions 

 the untrained person is unaware of the presence of such a sense; 

 but physiological analysis enables us to realize its existence. What 

 we designate as the feeling of resistance and of weight depends 

 usually partly upon the pressure sense, but largely upon the muscle 

 sense. As Head has pointed out (p. 259), we still possess a certain 

 sensibility to pressure, even after our cutaneous nerves are com- 

 pletely anesthetized, so that a pressure upon the skin is recognized 



