ELEMENTS OF ANATOMY

EDITED BY

EDWARD ALBERT SCHÄFER, F.R.S.

PROFESSOR OF PHYSIOLOGY AND HISTOLOGY IN UNIVERSITY COLLEGE, LONDON,

AND

GEORGE DANCER THANE,

PROFESSOR OF ANATOMY IN UNIVERSITY COLLFGE, LONDON.

IN THREE VOLUMES.

VOL. I.-PART I.

EMBRYOLOGY

BY PROFESSOR SCHÄFER.

ILLUSTRATED BY 200 ENGRAVINGS, MANY OF WHICH ARE COLOURED.

Tenth Edition.

LONDON:

LONGMANS, GREEN, AND CO.,

1890.

LIBRARY OF MEDICINE

FRANCIS A. COUNTWAY

BOSTON MEDICAL LIBRARY
IN THE

LONDON

BRADBURY, AGNEW, & CO. LIMD., PRINTERS, WHITEFRIAES,

ELEMENTS OF ANATOMY.

INTRODUCTION.

ANATOMY, in its most extended sense, is the science which deals with the structure of organized bodies. It is divided into departments according to its subjects; such as Human Anatomy; Comparative Anatomy, or the study of the structure of different animals; and Vegetable Anatomy, comprehending the structure of plants.

On examining the structure of an organized body, we find that it is made up of members or organs, by means of which its functions are executed, such as the root stem and leaves of a plant, and the heart, brain, stomach and limbs of an animal ; and farther, that these organs are themselves made up of certain constituent materials named tissues or textures, such as the cellular, woody, and vascular tissues of the vegetable, or the osseous, muscular, connective, vascular, nervous, and other tissues, which form the animal organs.

Most of the tissues occur in more than one organ, and some of them indeed, as the connective and vascular, in nearly all, so that a multitude of organs, and these greatly diversified, are constructed out of a small number of constituent tissues; and parts of the body, differing widely in form, construction, and uses, may agree in the nature of their component materials. Again, as the same tissue possesses the same essential characters in whatever organ or region it is found, it is obvious that the structure and properties of each tissue may be made the subject of investigation apart from the organs into whose formation it enters.

The foregoing considerations have led to the subdivision of anatomy into two branches, the one of which, under the name "General Anatomy," or "Histology," treats of the minute structure of the component tissues of the body; the other, named "Special or Descriptive Anatomy," treats of its several organs, members, and regions, describing the outward form and internal structure of the parts, their relative situation and mutual connection, and the successive conditions which they present in the progress of their formation or development.

To the description of the origin and formation of organs in the embryo, a special chapter is devoted in this work, under the name Embryology.

The study of anatomy may be viewed in two different aspects; viz., the physiological and the morphological. In the former, anatomy supplies the materials relating to structure from which an explanation is sought of the uses or functions of organs by the physiologist; and for this purpose the study of histology is of particular service. In its morphological aspect, anatomy investigates and combines the facts relating to the structure and relations of organs, from which may be deduced general principies as to the construction of the human body or that of

VOL. I.

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