rog6 



THE SENSES 



muscular movements. And it has been stated that paralysis of these 

 bodies in the limbs of a cat by section of the nerves going to them 

 causes a characteristic uncertainty of movement which suggests that 

 something necessary to normal co-ordination has been taken away. 

 Tendons also possess afferent nerve-fibres, which terminate by breaking 

 up into reticulated end-plates (Fig. 470). We have already seen that 

 the skeletal muscles possess numerous afferent fibres (p. 941). Some 

 of these must be nerves of ordinary sensation. For, although when a 

 muscle is laid ba: * in man and stimulated electrically, the sensation 

 does not in general amount to actual pain, it is capable, under the 

 influence of strong stimuli, of taking on a painful character. And 

 nobody who has felt the severe and sometimes almost intolerable pain 

 of muscular cramp would be likely to deny the existence of sensory 

 muscular nerves. But after deducting these, we must assume that a 





m'n.b. 



Fig. 448. Muscle Spindle (after Ruffini). c, sheath of the spindle ; n.tr., trunk 

 of nerve, which sends fibres through the sheath into the spindle, where they 

 form endings (pr.e., s.e., pl.e.) of various kinds; m.n.b.. bundle of motor fibres. 



large proportion of the afferent nerves of muscle have other functions, 

 and among them may be the conveyance of impulses connected with 

 the muscular sense. The muscle-spindles or neuro-muscular spindles 

 (Fig. 471), peculiar structures which occur in large number in most 

 of the skeletal muscles, and have been carefully studied by Huber, 

 Sihler, Ruffini, and other observers, are the terminations of many of 

 the sensory fibres. They are long narrow bodies, with a thick sheath 

 of connective tissue enclosing fine striped muscular fibres. Medul- 

 lated nerve-fibres enter the spindle, and there, dividing into branches 

 and losing their medullary sheath, form endings of various kinds around 

 and between the muscular fibres. It is possible that in contraction 

 of the muscles the nerve-fibres in the spindles are compressed, and thus 

 mechanically stimulated. 



In the spinal cord these impulses are conducted up through the 

 posterior column; and, although less is known as to the paths they 

 follow in the higher parts of the central nervous system, it is certain 

 that there is some afferent bond of connection between the cortical 

 motor areas and the muscles which they control (p. 963). 



Tactile sensations set up in the skin or mucous membrane lying 

 over contracting muscles may also help the nervous motor mechanism 

 in appreciating and regulating the amount of contraction ; but the fact 

 that, in anaesthesia of the mucous membrane covering the vocal cords 

 produced by cocaine, the voice is not at all impaired, shows that mus- 

 cular contractions of extreme nicety can be carried on without any 

 such aid. 



Sensations of Hunger and Thirst. These are representatives of 

 the group of interior sensations. As Tiedemann pointed out long 



