ANA'TOMY, from a Greek term which literally signifies the separation of a thing into parts by cutting;' the term Anatomy is used to signify particularly, dissection, or knowledge acquired by dissection. Anatomy is at once an art and a science ; an art, inasmuch RS the pursuit of it requires skilful manipulation ; and a science, inasmuch as certain general principles are deducible from it. The object of anatomy is to ascertain the structure of organised bodies. Of the two great kingdoms of nature, the inorganic and the organic, it comprehends the whole range of the latter. Like the organised kingdom itself, it forms two divisions, the one including the structure of plants—Vegetable Anatomy ; the other the structure of animals- Animal Anatomy. Animal Anatomy is divided into comparative and human : Comparative Anatomy includes an account of the structure of all classes of animals, excepting that of man ; Human Anatomy is restricted to an account of the structure of Irian only. Duman Anatomy is subdivided into descriptive, general, and pathological. Deseriptire Anatomy comprehends a description of all the various parts or organs of the human body, together with an account of their situation, connections, and relations, as these circumstances exist in the natural and sound, or, as it is technically termed, the normal, condition of the body. The human stomach, for example, is composed of a number of membranes, which are united in a particular manner; a number of blood-vessels which are derived from particular arterial trunks ; a number of nerves which proceed from a particular portion of the brain and spinal cord ; a number of absorbent vessels, and so on; moreover, this organ is always placed in a particular cavity of the body, and is always found to have certain specific connections or relations with other organs. The anatomy of the human stomach comprehends an account of all the particulars of this kind, which are uniformly found to concur in all human bodies in which the confor mation is regular or natural ; and so of every other organ •f the body : and because such an exposition of the structure of the various organs includes a description of all the circumstances that relate to their organisation, it is called Descriptive Anatomy.
After the study of the human body in this mode has been carried to a certain extent, with a certain degree of success, it necessarily gives origin to a second division of the science, that termed General Anatomy. It is found, that many of the circumstances which belong to any one organ, belong at the same time to several organs; and that thus several individual circumstances are common to many organs.
Of the membranes, for example, of which it has been stated that the stomach is composed, some are common to it and to the intestines, to the bladder, to the heart, to the air-passages, and so on. In like manner with respect to any one of these membranes, when its structure is carefully examined, it is found that in many points its organisation is exactly similar to that of all other membranes. This view extended leads to further important and interesting results. All the arteries of the body, whatever their situation, size, or office, are found to be composed essentially of the same substances, disposed in nearly the same order and form. All the veins have, in like manner, a structure essentially the same. All the absorbent vessels, all vessels of every kind, all the bones, muscles, and nerves, the whole external covering of the body or the skin, widely as these various structures differ from each other, present no material difference as far as regards the organisation of each particular class. Hence various organs of the body are disposed into what are called common systems, and these common systems are said to consist of common substances or tissues. All the vessels, for example, are collected and arranged under one common class, called the vascular system : in like manner, all the bones are collected and arranged under another class, called the osseous system ; all the muscles under another, called the mus cular system ; all the nerves under another, called the nervous system, and so on. The material that enters into the composition of each of these systems consists of a substance of a peculiar nature; but as this substance is more or less generally diffused over the whole body, entering as a constituent element into the various organs, it is termed a common substance, or tissue. What is termed the common cellular or areolar tissue, for example, is the substance which enters most commonly into the compositition of the organs of the body ; the muscular tissue is the substance of which the muscles are com posed ; the nervous tissue is the substance of which the nerves are composed : and thus, the structure of the body, analysed in this mode, innumerable and complex as the substances appear to be of which it consists, is ultimately reduced to a very few simple materials, by the combination and modification of which all the different animal substances are produced.