402 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



Recent researches have demonstrated the existence of an abundant supply 

 of sensory nerves, whose excitement must depend upon the exercise of 

 skeletal muscles. Ciaccio 1 has described the termination of sensory nerves 

 in tendons as a splitting up of the nerve-fibres whose axis-cylinders, in the 

 form of varicose threads, end freely as spirals or rings around the tendon- 

 bundles. The joints seem to be particularly rich in sensory nerve-supply. 

 Golgi - first described certain special modes of ending of sensory nerves just 

 at the junction of the voluntary muscle with its tendon. This terminal organ 

 is a fusiform corpuscle consisting of several delicate connective-tissue 

 envelope.- with nuclei, and is situated on the surface of the tendon. One to 

 several nerve-fibres enter each corpuscle, and, dividing and losing their 

 medullary sheaths, break up into an arborization of naked axis-cylinders. 

 The skeletal muscles themselves are extraordinarily rich in sensory nerve- 

 supply. According to Sherrington,' " the proportion of afferent-fibres to total 

 myelinate fibres ranges from a little more than one-third in some muscular 

 nerves to a full half in others." These sensory fibres end, for the most part, 

 in the so-called " muscle-spindles," which are fusiform bodies, usually just 

 visible to the unaided eye (Fig. 199, p. 390). The spindles are for the most 

 part scattered between the ordinary muscle-fibres, though many abut upon 

 intramuscular septa or are in the immediate vicinity of aponeuroses. As 

 many as thirteen spindles have been counted in one cross-section of thegenio- 

 glossus muscle. Sherrington ' calculates that the number of spindle-organs 

 is sufficient to account for nearly or quite two-thirds of all the afferent fibres 

 demonstrated to exist in the nerve-trunks of the limb muscles. It is worth 

 observing that the spindle-organs have not been demonstrated in the eve 

 muscles nor in the intrinsic muscles of the tongue. The muscle-spindle con- 

 sists of a central core of modified muscle-fibres inclosed in an outer capsule 

 formed of several layers of concentrically disposed membranous lamellae 

 composed of connective tissue. Between the capsule and the central muscle- 

 bundle is a wide lymph-space traversed by a network of delicate filaments. 

 In forming the spindle two or three ordinary muscle-fibres of the red variety 

 become invested at the proximal end of the organ by a definite sheath of 

 connective tissue. As they penetrate further into this envelope the muscle- 

 fibres tend to split lengthways, each fibre giving rise to perhaps three 

 " daughter "-fibres, which are proportionally of less diameter. The striatum 

 and fibrillation are frequently confined to the outer portion of these daughter- 

 fibres, some of which are devoid of sarcolemma. For the middle third of 



its course in the muscle-spindle each daughter-fibre bei es thickly crusted 



with a sheet of nuclei. Toward the distal end of the spindle the muscle- 

 fibres often merge in tendon-bundles, which finally combine with the fibrous 

 tissue forming the capsule of the spindle ; so that of the two ends of the axial 

 bundle within the spindle, one is muscular and the otheris tendinous. 



According to Rufrini/' sensory nerves may end upon the axial muscle- 



1 Barker: The Nervous System, 1899, |>. 105 - Ibid. 



3 Sherrington : Journal of Physiology, L895, vol. xvii. p. 229. 4 Ibid. 



5 Ruffini : Ibid., 1898, sxiii. 190. 



