440 THE ORGANS 



From this network capillaries enter the corpuscle, usually near the 

 nerve fibre, and penetrate among the lamellae, even reaching the 

 distal end of the corpuscle. They do not enter the inner bulb. 

 The Pacinian bodies are found in the subcutaneous fat, especially 

 of the hand and foot, in the parietal peritoneum, mesentery, penis, 

 clitoris, urethra, nipple, mammary gland, in the vicinity of tendons, 

 ligaments and joints. 



In voluntary muscle afferent nerves terminate in Pacinian cor- 

 puscles, in end bulbs, and in complicated end organs called muscle 

 spindles, or neuromuscular bundles. The muscle spindle (Fig. 308) 

 is an elongated cylindrical structure within which are muscle fibres, 

 connective tissue, blood-vessels, and medullated nerves. The 

 whole is enclosed in a connective-tissue sheath which is pierced at 

 various points by nerve fibres. A single spindle contains several 

 muscle fibres and nerve fibres. The muscle fibres differ from ordi- 

 nary fibres, being fine and containing more nuclei and sarcoplasm in 

 the middle. The muscle spindles are more numerous in the limb 

 muscles than in those of the trunk, and in the distal than the 

 proximal part of the limb. There are few in eye muscles and in 

 some muscles they have not been detected. According to Ruffini, 

 there are three modes of ultimate terminations of the nerve fibres 

 within the spindles: one in which the end fibrils form a series of rings 

 which encircle the individual muscle fibre, termed annular termina- 

 tions; a second in which the nerve fibrils wrap around the muscle 

 fibres in a spiral manner — spiral terminations; a third in which the 

 terminations take the form of delicate expansions on the muscle 

 fibre — arborescent terminations. 



At the junction of muscle and tendon are found the elaborate 

 afferent terminal structures, known as the muscle-tendon organs of 

 Golgi (Fig. 309). This is a spindle-shaped body composed of several 

 tendon bundles. Into this there enter one or several nerve fibres 

 which break up into complicated terminal arborizations upon the 

 tendon bundles. 



Other forms of nerve endings enclosed within connective-tissue 

 sheaths are corpuscles of Ruffini found in the subcutaneous tissue 

 of the finger and corpuscles of Golgi-Mazzoni found on the surfaces 

 of tendons and also in the subcutaneous tissue of the fingers and in 

 other parts of the skin. 



It is evident from the above that the nerve terminations are onlj' stimulated 

 through the intermediation of surrounding cells which may form quite elab- 



