INTRODUCTION
Anatomy is the branch of biological science which deals with the form and structure of organisms, both animal and vegetal. It is therefore in close correlation with physiology, which treats of the functions of the body.
Etymologically the word “anatomy” signifies the cutting apart or disassociating of parts of the body. In the earlier phases of its development anatomy was necessarily a purely descriptive science, based on such observations as were possible with the unaided eye and simple dissecting instruments—the scalpel, forceps, and the like. At this time, therefore, the term adequately expressed the nature of the subject. But as the scope of the science extended and the body of anatomical knowledge grew, subdivisions became necessary and new terms were introduced to designate special fields and methods of work. With the introduction of the microscope and its accessories it became possible to study the finer details of structure and minute organisms hitherto unknown, and this field of inquiry rapidly developed into the science of microscopic anatomy or histology as conventionally distinguished from gross or macroscopic anatomy. In the same way the study of the changes which organisms undergo during their development soon attained sufficient importance to be regarded on practical grounds as a separate branch known as embryology.
This term is usually limited in its application to the earlier phases of development during which the tissues and organs are formed. The term ontogeny is used to designate the entire development of the individual. The ancestral history or phylogeny of the species is constituted by the evolutionary changes which it has undergone as disclosed by the geological record.
Comparative anatomy is the description and comparison of the structure of animals, and forms the basis for their classification. By this means—including extinct forms in the scope of inquiry—it has been possible to show the genetic relationship of various groups of animals and to elucidate the significance of many facts of structure which are otherwise quite obscure. The deductions concerning the general laws of form and structure derived from comparative anatomical studies constitute the science of morphology or philosophical anatomy. The morphologist, however, deals only with such anatomical details as are necessary to form a basis for his generalizations. The anatomical knowledge required in the practice of medicine and surgery is evidently of a different character and must include many details which are of no particular interest to the morphologist.
Special anatomy is the description of the structure of a single type or species, e. g., anthropotomy, hippotomy.
Veterinary anatomy is the branch which deals with the form and structure of the principal domesticated animals. It is usually pursued with regard to professional requirements, and is therefore largely descriptive in character. As a matter of convenience the horse is generally selected as the type to be studied in detail and to form a basis for comparison of the more essential differential characters in the other animals.
Two chief methods of study are employed—the systematic and the topographic. In the former the body is regarded as consisting of systems of organs or apparatus which are similar in origin and structure and are associated in the performance of certain functions. The divisions of systematic anatomy are:
- 1.
- Osteology
- 2.
- Arthrology
- 3.
- Myology
- 4.
- Splanchnology
- (1)
- Digestive System
- (2)
- Respiratory System
- (3)
- Urogenital System
- (a) Urinary Organs
- (b) Genital Organs
- 5.
- Angiology
- 6.
- Neurology
- 7.
- Æsthesiology
- (1)
- Sense Organs
- (2)
- Common Integument.
The term topographic anatomy designates the methods by which the relative positions of the various parts of the body are accurately determined. It presupposes a fair working knowledge of systematic anatomy.
Descriptive Terms.—In order to indicate precisely the position and direction of parts of the body, certain descriptive terms are employed, and must be understood at the outset. In the explanation of these terms it is assumed here that they apply to a quadruped such as the horse in the ordinary standing position. The surface directed toward the plane of support (the ground) is termed inferior or ventral, and the opposite surface is superior or dorsal; the relations of parts in this direction are named accordingly. The longitudinal median plane divides the body into similar halves. A structure or surface which is nearer than another to the median plane is internal or medial to it, and an object or surface which is further than another from the median plane is external or lateral to it. Planes parallel to the median plane are sagittal. Transverse or segmental planes cut the long axis of the body perpendicular to the median plane, or an organ or limb at right angles to its long axis. A frontal plane is perpendicular to the median and transverse planes. The head end of the body is termed anterior, cephalic, or cranial; and the tail end posterior or caudal; relations of structures with regard to the longitudinal axis of the body are designated accordingly. Certain terms are used in a special sense as applied to the limbs. Proximal and distal express relative distances of parts from the axis of the body. The anterior face of the thoracic limb from the elbow downward is also termed dorsal, and the opposite face volar. In the corresponding part of the pelvic limb the terms are dorsal and plantar respectively. In the same regions radial and ulnar (thoracic limb), tibial and fibular (pelvic limb), may be used to designate that side of the extremity on which the corresponding bone is situated; they are therefore equivalent respectively to internal or medial and external or lateral in the animals with which we are concerned.
It is evidently advantageous to employ terms which are as far as possible independent of the position of the body in space and capable of general application, e. g., dorsal, ventral, proximal, etc. It is also desirable that the terms internal and external be reserved to indicate relations of depth in cavities or organs, and medial and lateral to designate relations to the median plane. Such terms are coming into more extensive use in human and veterinary anatomy, but the older nomenclature is very firmly established and cannot well be discarded at once and entirely.