770 PHYSIOLOGY. 



reflex between the semicircular canals and the muscles of the body 

 innervated by the anterior horns which have the vestibulo-spinal 

 tract connected with them. 



The fibers from Deiters's nucleus go to the nuclei of the motor 

 nerves of the eye by the posterior longitudinal bundle; hence the 

 nucleus of Deiters may be a reflex center, with the semicircular canal 

 on one side and the fibers from Deiters's nucleus to the motor nuclei 

 for the eye-muscles on the other side. Destruction of the semicircular 

 canals would thus cause loss of tonus in the eye-muscles. 



Fig. 320. Position of Pigeon's Head after removal of all the semi- 

 circular canals on both sides. (EwALD, J. R.) (From Tigerstedt's 

 "Human Physiology," copyright, 1906, by D. Appleton and Company.) 



A 20-gram lead ball fastened to beak with wax, which cannot be moved, owing 

 to weakness of the muscles of the neck. 



TJtriculus and Sacculus. The utriculus and sacculus, small sacs, 

 also contain hair-cells, and lying among them are the otoliths, con- 

 sisting of crystals of calcium carbonate. Breuer states that these sacs 

 give us information when the head is at rest and when it is making 

 slow rotary movements. Thus they aid the function of the semicir- 

 cular canals. In this view, the otoliths mechanically stimulate the 

 hairs. 



