PEEFACE TO THE TWENTIETH EDITION. 



SINCE the publication of the first English edition of this \vork in 1858 and the 

 first American edition in 1859 great advances in the subject of Anatomy have been 

 made, especially in microscopic anatomy and the anatomy of the embryo. This 

 knowledge was embodied from time to time in the successive editions until finally 

 considerable portions of the text, sometimes sections, were devoted to these sub- 

 jects. However, the main text has always remained primarily a descriptive 

 anatomy of the human body. 



In the present edition the special sections on embryology and histology have 

 been distributed among the subjects under which they naturally belong. New 

 matter on physiological anatomy, laws of bone architecture, the mechanics and 

 variations of muscles have been added, occupying much of the space formerly 

 devoted to the sections on applied anatomy. 



The sections on the ductless glands and the nervous system have been largely 

 rewritten. In the latter a more rational presentation of the sympathetic nervous 

 system has been achieved through the use of diagrams and descriptions based on 

 physiological and pharmacological work. The central connections of 'the spinal 

 and cranial nerves are also emphasized. 



Illustrations have been added wherever important points could be made more 

 clear, and throughout the work colored pictures have been even more extensively 

 used than heretofore. In this respect special mention might be made of the central 

 nervous system and the section on the muscles. In the section on Syndesmology 

 six illustrations are used from Quain's Anatomy through the courtesy of the 

 publishers, Messrs. Longmans, Green & Company, of London. 



The use of the B. N. A. nomenclature in English has been retained practically 

 unchanged in this edition and important references to the literature have been 

 added at the end of each section. 



As a practical work on the subject for the student, Gray's Anatomy has always 

 been recognized and appreciated. The plan originally formulated, which has 

 proved so successful, has been adhered to as much as possible. It is interesting to 

 note that although Henry Gray saw only the first edition, much of the original 

 text persists and many of his illustrations are still in use. Bearing this in mind it 

 has been the endeavor of the Editor to supply only such changes as advances in 

 the science made necessary in order that this work may reflect the latest accessions 

 to anatomical knowledge. 



W. H. L. 



BALTIMORE, 1918. 



