INTRODUCTION 



By C. M. JACKSON, M.S., M.D. 



PROFESSOR OF ANATOMY, UNIVERSITT OP MINNESOTA. 



A NATOMY, as the term is usually employed, denotes the study of the 

 /\ structure of the human bod^^ Properly, however, it has a much wider 

 ^-^ significance, including within its scope not man alone, but all animal forms, 

 and, indeed, plant forms as well; so that, when its application is limited to man, 

 it should be qualified by the adjective human. Human Anatomy, then, is the 

 study of the structure of the human body, and stands in contrast to, or rather in 

 correlation with, Human Physiology, which treats of the functions of the human 

 body, the two sciences. Anatomy and Physiology, including the complete study 

 of man's organization and functional activities. 



In the early historj^ of the sciences these terms sufficed for all practical needs, 

 but as knowledge grew, specialization of necessity resulted and new terms were 

 from time to time introduced to designate special lines of anatomical inquiry. 

 With the improvement of the microscope a new field of anatomy was opened up 

 and the science of Histology came into existence, assuming control over that 

 portion of Anatomy which dealt wdth the minuter details of structure. So, too, 

 the study of the development of the various organs gradually assumed the 

 dignity of a more or less independent study known as Embryology , and the study 

 of the structural changes due to disease was included in the science of Pathology; 

 so that the term Anatomy is sometimes limited to the study of the macroscopic 

 structure of normal adult organisms. 



It is clear, however, that the fines of separation between Anatomy, Histolog}", 

 Embryology, and Pathology are entirely arbitrary. Microscopic anatomy 

 necessarily grades off into macroscopic anatomy; the development of an organism 

 is a progressive process and the later embryonic or foetal stages shade gradually 

 into the adult; and structural anomalies lead insensibly from the normal to the 

 pathological domains. Furthermore it is found that in its individual develop- 

 ment the organism passes through stages corresponding to those of its ancestry 

 in evolution; in other words, Ontogen}^ repeats Phylogeny. A comprehensive 

 study of Anatoni}^ must therefore include more or less of the other sciences, and 

 since an appreciation of the significance of structural details can onl}^ be obtained 

 by combining the stucfies of Anatomy, including Histology and Embryology, 

 and since, further, much light may be thrown on the significance of embryological 

 stages by comparative studies, Anatomy, Embrj-ology, and Comparative Anatomy 

 form a triumvirate of sciences by which the structure of an organism, the signi- 

 ficance of that structure, and the laws which determine it are elucidated. For 

 this combination it is convenient to have a single term, and that which is used is 

 Morphology, a word meaning literally the science of form. 



In morphological comparisons, the term homology denotes similarity of structure, due to a 

 common origin in the evolution of organs or parts; while analogij denotes merely physiological 

 correspondence in function. Thus the arm of man and the wing of a bird are homologous, but 

 not analogous, structures; on the other hai^d, the wing of a bird and the wing of an insect are 

 analgous, but not homologous. Serial homology refers to corresponding parts in successive 

 segments of the body. 



Nomenclature. — Formerly there was much confusion in the anatomical 

 nomenclature, due to the multiphcity of names and the lack of uniformity in 

 using them. Various names were appfied to the same organs and great diversity 

 of usage prevailed, not onl}^ between various countries, but also even among 

 authors of the same country. Recently, however, a great improvement has been 

 made by the general adoption of an international system of anatomical nomen- 



