918 CENTRAL NERVOUS SYSTEM 



prioceptors of the muscles and tendons, and in part from the labyrinth. 

 The former are influenced by the position of the parts of the body, the 

 latter by the position of the body as a whole in space. The attitude con- 

 sequently depends* not only on the harmonious a'djustment of the posture 

 of its parts, but all these are brought into relation with the position 

 of the body in space, whether right side up, inverted, etc. The in- 

 teraction of these two sets of proprioceptors is illustrated by ex- 

 periments on the decerebrate cat. The tone of the extensors of such 

 animals is sufficient to support the body's weight. If the head of the 

 standing animal is forcibly flexed, the postural contraction of the ex- 

 tensor muscles of the fore limbs is inhibited, and the forequarters sink, 

 while at the same time the postural contraction of the extensor muscles 

 of the hind limbs increases, raising the hind quarters. The animal as- 

 sumed the appropriate attitude for looking under a shelf. On the other 

 hand, if the head is passively tilted up and back, the postural contrac- 

 tion of the extensor muscles of the fore limbs increases, raising the fore 

 quarters, and at the same time the postural contraction of the extensors 

 of the hind limbs is diminished so that the hind limbs sink. The at- 

 titude is now that of a cat looking up at a shelf. These reactions per- 

 sist after the labyrinths have been destroyed and consequently must 

 be due to proprioceptors in the muscles of the neck. The influence of 

 the labyrinth was studied by rendering the neck immobile with a plas- 

 ter cast, or by cutting the afferent roots of the upper cervicle nerves. 

 On changing the position of the head the same adjustments occurred 

 in the position of the limbs, so that the labyrinth must reinforce the 

 proprioceptors of the neck in their action. In addition the labyrinth 

 affected the posture of the neck in such a way that it would, had its 

 afferents been intact, have set up the appropriate change in the limb 

 posture. It has long been known that destruction of the labyrinth causes 

 very abnormal postures to be assumed and these can be attributed to 

 unusual positions set up in the neck muscles. In case of destruction of 

 both labyrinths a great loss in tone results. If the organ on one side 

 only is destroyed, tone is diminished on the opposite side, with the re- 

 sult that the trunk is curved and the animal tends to roll over and over. 

 Compensatory Movements of the Eyes, The position of the eyes is 

 very markedly influenced by stimulation set up in the labyrinth. This is 

 of obvious importance, since as our bodies move, compensation must be 

 made by the eye muscles in order that the gaze may remain fixed on any 

 object. This relationship is nicely demonstrated in the dogfish where 

 the labyrinth is large and easily experimented upon. As the head of the fish 

 is turned from side to side, as it is in swimming, the eyes move so as 

 to compensate for the change in position. When the head turns to the 

 left the left eye is turned forward, the right eye backward so as to re- 



