2l8 NERVOUS FIBRILS OF EYE, EAR, ETC. 



from end to end, some longitudinal fibres run- 

 ning between them. 



In the intestines a peculiar molecular arrange- 

 ment of nerve and muscle is also found, as well 

 as circular and longitudinal fibres, which are con- 

 tinuous from the czsophagus to the rectum. This 

 motion of the intestines is called the peristaltic, or 

 churning motion ; and without doubt is another 

 manifestation of the periodic impulse. 



The eye is protected by a strong membranous 

 covering. The rods and cones are its distinctive 

 molecular arrangement. A single nervous fibril 

 runs^from each of these cones through the trunk 

 of the optic nerve to the brain separately from 

 its neighbors, effecting a direct and continuous 

 connection with the brain. As this peculiar 

 molecular arrangement differs from those of the 

 heart and intestines, we may naturally infer that 

 the periodic excitation transmitted to the eye 

 produces there a distinctive motion. 



In the ear we find that electric vibrations are 

 gradually changed into currents by the action of 

 the ossicles, in passing from the external ear to 

 the brain, and that the connection is continuous. 

 These ossicles in the drum, and Corti's rods and 

 arches in the cochlea, form the peculiar molecular 

 arrangements of the ear; and we may infer that 

 the periods of rhythmic flow and rest penetrate 

 this strange musical gallery, making its chords 

 respond more quickly and sympathetically to the 

 electric vibrations that sweep over them. 



