264 THE SPECIAL SENSES. 



for this misreference is that the pain is referred to the skin region 

 that is supplied from the spinal segment from which the organ in 

 question receives its sensory fibers, the misreference being due to a 

 diffusion in the nerve centers. As Head expresses it, "when a 

 painful stimulus is applied to a part of low sensibility in close central 

 connection with a part of much greater sensibility the pain produced 

 is felt in the part of higher sensibility rather than in the part of lower 

 sensibility to which the stimulus was actually applied.' ' It is 

 interesting that affections of the serous cavities e.g., the peritoneum 

 do not cause reflected pains or cutaneous tenderness as in the 

 case of the viscera. Another notable fact in this connection is the 

 occurrence of the condition known as allochiria. When from any 

 cause one or other of the cutaneous senses is depressed in a given 

 area stimulation in this region may give sensations which are re- 

 ferred to the symmetrical area on the other side of the body, or, if 

 this also is involved, it may be referred to the area next above or 

 below in the spinal order. The above law, according to which pro- 

 jection is made to the area of higher sensibility most closely con- 

 nected with the area of low sensibility, seems to hold in this case 

 also. 



The Muscle Sense. The existence of a special set of sensory 

 nerve fibers distributed to the muscles was clearly recognized by 

 some of the older physiologists. Charles Bell,* for example, says: 

 "Between the brain and the muscles there is a circle of nerves; one 

 nerve conveys the influence from the brain to the muscle; another 

 gives the sense of the condition of the muscle to the brain." The 

 conclusive proof of the existence of such fibers, however, has only 

 been furnished within recent years. It has been demonstrated 

 that there are special sensory endings in the muscles, the so-called 

 muscle spindles, and in the attached tendons, the tendon spindles 

 or tendon organs of Golgi. The muscle spindles are found most 

 frequently in the neighborhood of the tendons, at tendinous inter- 

 sections or under aponeuroses. Sherrington! has shown that the 

 nerve fibers in them do not degenerate after section of the anterior 

 roots of the corresponding spinal nerves and are therefore derived 

 from the posterior roots. In the muscles of the limbs he estimates 

 that from one-half to one-third of the fibers in the muscular nerve 

 branches are sensory, and that most of these sensory fibers end in 

 the muscle spindles. On the physiological and clinical side facts of 

 various kinds have accumulated that make clear the existence of 

 this group of sensory fibers and emphasize their essential importance 

 in the co-ordination of our muscular movements. It has been shown 



* Bell, "The Nervous System of the Human Body," third edition, Lon- 

 don, 1844, p. 200. 



f Sherrington, "Journal of Physiology," 17, 237, 1894. 



