ioo6 THE MUSCULAR SENSE. 



is the very slight impairment of muscular sense which follows cutaneous 

 ansesthesia ; and the very great impairment following injury to the deep 

 sensory nerves of a limb, in spite of visual assistance. 



There remains, then, a third view, namely, that the muscular sense 

 is based on a specific set of sensations obtained by specific sense organs 

 in muscles, tendons, joints, and all the accessory organs of movement. 

 To this view adherence is given in the following account. 



Charles Bell l was the first to definitely postulate the existence of a 

 muscular sense on a physiological parity with the other senses. After his 

 writings it began to be referred to as the sixth, sense. He was not, of course, 

 the first to suppose that consciousness of the positions and movements of the 

 body and of its parts is based on sensations. Neither did he, in speaking of 

 " muscular sense," suggest that the muscles are the exclusive site of origin of its 

 sensations ; but he was the first to postulate the existence of special afferent peri- 

 pheral nerves for impulses evoked by the movements and postures of the body. 



It is obvious that any extensive action of the skeletal musculature 

 must, when it occurs, affect various organs of sense. Such effects 

 may be separated into " resident " and " remote." 2 The hand when 

 moved at the wrist-joint provokes mechanically, by tensions and re- 

 laxations of muscles and of their tendons, ligaments, and the like, a 

 number of sensory end-organs belonging to those structures. It also 

 affects, by stretching and flexing the skin, sense organs within it. If 

 the movement bring the part against an object, or against another 

 part of the subject, touch, and in the latter case the so-called " double 

 touch," results. Its movement may bring the part moved into the field 

 of vision. These last-named tactual and visual effects constitute the 

 " remote " results ; on the contrary, the sensations of muscle and joint 

 in fact, of the motor organs in play are the " resident " effects. 



We may treat of the muscular sense as of other senses. The parts of 

 its apparatus may be distinguished as peripheral, internuncial, and 

 central ; among its phenomena may be distinguished centripetal impulses, 

 sense impressions, sense perceptions, judgments, and ideas. 



THE PERIPHERAL APPARATUS OF THE MUSCULAR SENSE. 



Under this heading may be included the afferent nervous apparatus 

 of the locomotor organs, muscles, joints, and bones. Evidence that 

 structures are afferent may be indirect, e.g. inferred from histology, or 

 direct, obtainable by physiological experiment. To begin with the 

 histological evidence. 



Nerves of bone. Bones are indubitably well supplied with nerves, the 

 long, the short, and the flat bones alike. The nerve fibres are derived, 

 according to Kolliker's 3 summary, from the spinal roots and from the sym- 

 pathetic. One-third of the fibres measure above 10 /x diameter. They 

 " branch and end in a manner that quite recalls the behaviour of sensory 

 spinal fibres " (Kolliker). 4 In my degeneration experiments on the nerves 

 of the limb, I found many sound myelinated fibres in the nerve perforating 

 the tibia, though all motor root fibres and all sympathetic myelinated fibres 

 had been destroyed by degeneration. 5 



Periosteum. The periosteum is supplied with nerves, though sparsely. 



1 Phil. Trans., London, 1830. 



2 W. James, "Principles of Psychology," London, 1891, vol. ii. p. 494. 



3 " Handbuch d. Gewebelehre," 1889, Bd. i. 4 Ibid., S. 313. 

 6 Sherrington, Journ. Physiol., Cambridge and London, 1894, vol. xvii. 



