TO THE READER. 



Tecis Lecture appears as it would have been delivered 

 had the time allowed been less strictlj limited. Passages 

 necessarily omitted have been restored, and points briefly 

 touched have been more fully considered. A few notes 

 have been added for the benefit of that limited class of 

 students who care to track an author through the high- 

 ways and by-ways of his reading. I owe my thanks to 

 several of my professional brethren who have communi- 

 cated with me on subjects with which they are familiar ; 

 especially to Dr. John Dean, for the opportunity of profit- 

 ing by his unpublished labors, and to Dr. Hasket Derby, 

 for information and references to recent authorities relating 

 to the anatomy and physiology of the eye. 



