EYE OF THE ENGLISH SPARROW 415 



tion the force necessary to change its shape is far greater than is 

 possible in the ciliary muscles. Again the only attachment of 

 the lens is to the ciliary bodies at the annular pad. The annular 

 pad is attached so loosely to the lenticular portion of the lens 

 that even a slight pull would cause a separation of these two 

 parts of the lens at the lenticular chamber rather than change 

 the shape of the firm spherical center. The ligamentum pecti- 

 natum which joins the ciliary bodies and iris can, in my opinion, 

 play no part in changing the shape of the lens. 



After a careful study of the anatomy of the structures in- 

 volved, in both fresh and preserved material, and experimenta- 

 tion on the living tissues, I am forced to conclude that accom- 

 modation in the bird must be accomplished in a very different 

 manner from what it is in man. All the evidence leads me 

 further to conclude that changes in accommodation in the spar- 

 row are associated with changes in the axial diameter, position 

 of the lens, and curvature of the cornea, and that these alone 

 are sufficient to secure clear vision at different distances. 



THE PECTEN 



Although the pecten is not derived directly from the chorioid, 

 it is described here because of their common origin, both arising 

 from the embryonic mesenchyme. 



In the sparrow the pecten is attached to the optic disc through- 

 out its entire extent. Its position and relative extent is shown 

 in fig. 1, P, plate 1. The optic nerve enters at Op and extends 

 downward and forward to near the ora serrata, a distance of 

 about 2.7 mm. Figure 14, plate 3, shows how near the distal, 

 basal portion of the pecten comes to the ora serrata. It also 

 shows the close relationship of the distal free margin to the 

 ciliary region and the lens. 



The pecten appears as a dark-brown, or black, fluted mass 

 (Virchow, '00), completely covering the optic disc except where 

 the nerve first enters the eye. It extends out into the vitreous 

 body in a plane almost parallel with the path of light entering 

 through the center of the pupil. Its widest extent in this direc- 



