CUTANEOUS AND INTERNAL SENSATIONS. 285 



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 apparently withdrawn from voluntary control in spite of the 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 afferent nerve-fibers of the muscles 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 central 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 afferent element 

 in the reflex cerebellar control of muscular movements, particularly 

 of the synergetic combinations necessary in locomotion. Through 

 the circle or arc in the cortex of the cerebrum it may be supposed 

 that our characteristic voluntary movements are affected, 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 afferent impulses 

 along the fibers of muscle sense. We have a certain conscious- 

 ness 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 Muscular Sensibility. — Under the term 

 muscular sensibility in its wide sense we must understand the 

 sensibility mediated by the afferent fibers from the muscles, 

 the tendons, ligaments, and joints. The quality of these deep 

 sensations is of several kinds — we have first of all the deep 

 pressure sensibility (see p. 275), which gives a definite conscious 

 reaction that is well localized. It is usually projected to the 

 exterior and is not consciously separated from the tactile or 

 pressure sensations of the skin. We probably make much use 

 of this sensibility in judging the weight and resistance of bodies. 

 Muscular sensibility proper is that ill-defined consciousness 

 which we possess of the condition and position of our muscles 



