The following illustrations have been copied from Quain's 

 "Anatomy" and Schiifer's "Essentials of Histology," and 

 are used in this work by permission of the authors and pub- 

 lishers of those books, viz. : Figs. 4, 5, 8, 10, 12, 14, 51, 53, 64, 

 69, 83, 86, 103, 110, 117, 121, 127, 128. 



