PEEEACE. 



The principal object in view, in the following memoir, has been to give the entire 

 topography of the meduUa oblongata and trapezium, with illustrations from a series 

 of photographs, the negatives of which have been prepared solely by myself, and 

 have in no case received any retouching. Over two years of constant study have 

 been devoted solely to this investigation, the results of which, both descriptive and 

 histological, I have constantly endeavored to render as trustworthy as possible. 



It was my original intention to comprise, in the same communication, the anatomy 

 of the pons Varolii, including that part of the human pons corresponding to the 

 trapezium. Such a plan, however, would have been attended with many diffi- 

 culties, besides a great increase in the number of illustrations, and it has therefore 

 seemed best to present the second part of this paper in a form which I am well 

 aware is quite incomplete, with the hope of extending it at some future time. 



A limited number of photographic prints from the original negatives have been 

 prepared by myself for private distribution, and from these negatives other copies 

 may be obtained, which wUl be supplied, as far as possible, either on direct applica- 

 tion to the author or through the medium of the Smithsonian Institution. 



For the labor and patience bestowed on the photo-lithographs by Mr. L. H. 

 Bradford, and for the conscientious care and skiU with which Mr. J. W. Watts has 

 engraved my histological drawings, I owe and gladly render my most grateful 

 thanks. 



JOHN DEAN. 

 11 Louisburg Square, Boston. 



