784 THE SENSE OF EQUILIBRIUM 



are shifted, so that the different hairs are mechanically acted upon 

 with varying force. Furthermore, it should be noted that the maculae 

 acusticse occupy different planes in space so that they are affected 

 differently by one and the same position, or progressive movement. 

 These statolithic receptors supplement the function of the receptors 

 in the ampullae of the semicircular canals which, as will be shown later, 

 mediate the sensations of rotatory motion and are, therefore, primarily 

 concerned with the production of the dynamic sense. In both cases, 

 these sensations give rise to reflexes which are essential for the main- 

 tenance of the equilibrium. Obviously, these reflexes initiate first 

 of all certain muscular movements, which are executed in compensa- 

 tion for these static and dynamic sensations. In last analysis, how- 

 ever, the static and dynamic senses are compound in their nature, 

 because they depend not only upon the sensations derived from the 

 corresponding sensory structures of the labyrinth, but also upon those 



Fig. 397. — Organ of Golgi from Human Tendo Achillis. Chlorid of Gold Prepa- 

 ration. (Ciaccio.) 

 m, Muscular fibres; t, tendon-bundles; g, Golgi's organ; n, two nerve-fibres passing 

 to it. 



obtained from the retinae, from the cutaneous receptors, and, as will 

 be shown later on, from the deep receptors situated in the muscles, 

 joints and tendons. 



It is also to be noted that these organs of equilibrium are thoroughly 

 protected against all direct influences from without, i.e., their activa- 

 tion can only be effected by changes arising within the animal itself. 

 For this reason, the static and dynamic sense-organs are commonly 

 regarded as belonging to the proprioceptive system of receptors. 

 Furthermore, since the static and dynamic senses are really compound 

 senses, because amplified and perfected by sensations received from 

 other sense-organs, such as the retinae and the cutaneous corpuscles, 

 their development actually necessitates a harmonious interaction 

 between different exteroceptors and proprioceptors. 



The Muscle Spindles. — It is a well-known fact that the muscles 

 and tendons as well as the lining of the joints and the deep skin are 



