CUTANEOUS AND INTERNAL SENSATIONS. 265 



that stimulation of the nerves distributed to the muscles or mechani- 

 cal stimulation of the muscles themselves causes a depressor effect 

 upon blood-pressure, thus demonstrating the presence of afferent 

 fibers in the muscles. As described in the section upon the central 

 nervous system, the numerous experiments upon the effect of section 

 of the posterior and lateral columns of the cord and observations 

 upon the results of pathological lesions of the posterior columns 

 (tabes dorsalis) give results which are interpreted to mean that fibers 

 of muscular sensibility form the most important group in the 

 posterior columns and constitute, as well, perhaps, the long, ascend- 

 ing fibers in the tracts of Flechsig and Gowers in the lateral col- 

 umns. It is believed, therefore, that our so-called voluntary muscles 

 are richly supplied with afferent fibers and that the impulses carried 

 by these fibers to the brain are necessary for the proper contraction 

 of the muscles and particularly for the adequate combination of 

 the contractions of groups of muscles in the co-ordinated movements 

 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 they are apparently withdrawn from voluntary control in spite of 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 are traced into the 

 nuclei of Goll and of Burdach in the medulla and thence partly into 

 the cerebellum and partly into the cerebrum by way of the median 

 fillet. Within 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 voluntary 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 



