PREFACE. Xi 



rian Museum gave mc permission to take such draw- 

 ings of the preparations it contains^ as I miglit want 

 for the illustration of this work; and to Mr. Clift, tlic 

 conservator, and Mr. Owen, the assistant conservator 

 of the museum, for their ohliging assistance on this 

 occasion. Mere verbal description can never con- 

 vey distinct ideas of the form and structure of parts, 

 unless aided by figures; and these I have accordingly 

 introduced very extensively in the course of the 

 work.^ 



Being compelled, from the nature of my subject, 

 and in order to avoid tedious and fatiguing circum- 

 locution, to employ many terms of science, I have 

 been careful to explain the meaning of each when first 

 introduced: but as it might frequently happen that, 

 en a subsequent occurrence, their signification may 

 have been forgotten, the reader will generally find in 

 the index, which I have, with this view, made very 

 copious, a reference to the passage where the term is 

 explained. 



I beg, in this place, to express my deep sense of 

 the obligation conferred on me by Mr. Davies Gil- 

 bert, the late president of the Royal Society, to whose 

 kindness I owe my being appointed to write this 

 treatise. 



* All the wood engravings have been executed by Mr. Byfield, and the 

 drawuigs for them were, for tlie most part, made by Miss Catlow, whose as- 

 sistance on this occasion has been most valuable to me. 



