EYE OF THE ENGLISH SPARROW 413 



and by means of the firm attachment of the ciUary processes to 

 the lens, the latter would be drawn back to its passive position. 

 Conditions are now favorable for distinct vision of distant 

 objects. To a certain extent the process of accommodation 

 resembles that of focusing a camera. The almost spherical lens 

 would require very little forward and backward movement to 

 accommodate for near and far vision. 



This theory of accommodation in the bird is partly proved 

 by the following experiment. A sparrow was anesthetized and 

 its ciliary muscles stimulated by an interrupted Faradic current. 

 The electrodes were applied to the eye in the region of the ciliary 

 nerve plexus. Each time the stimulus was applied all the ciliary 

 muscles were thrown into a tetanic contraction. With each 

 stimulus the cornea, iris, and lens moved very noticeably for- 

 ward. The lens seemed to have a greater amplitude of move- 

 ment than the cornea, but the curvature of the latter was in- 

 creased. When the stimulus ceased these parts quickly resumed 

 their original positions. These observations were confirmed 

 independently by a disinterested person called in to state what 

 he saw when the stimulus was applied. This experiment proves 

 that the eye of the sparrow, in the resting condition, is appar- 

 ently adjusted for far vision. In other words, distant vision is 

 a passive act and near vision requires the contraction of the 

 muscles of accommodation. 



The value of striated muscle fibers in the ciliary muscles can 

 readily be appreciated when one considers the extremely rapid 

 flight of the bird. The rapidity with which numerous objects 

 confront the bird is almost beyond conception. And yet I 

 have never seen a bird in its flight among trees and shrubbery 

 have a collision. The power of rapid accommodation must 

 reach such a degree of perfection in the bird as will enable it to 

 see quickly approaching objects with sufficient distinctness to 

 avoid collision. Such rapid changes in accommodation would 

 not be possible were the ciliary muscles composed of smooth 

 muscle fibers as in man. 



This theory of accommodation in the bird eye is different from 

 that advanced by most writers. Some have thought that the 



THE JOURNAL OF MORPHOLOGY, VOL. 31, NO. 3 



