COMPARATIVE ANATOMY is a term, now obsolescent, applied to the study of the structure of diverse animals, intended to bring out their differences and resemblances. It arose as a separate science in the i 6th century, although the most important generalization which has resulted from it was tacitly assumed by those earlier anatomists who, unable to dissect human bodies, made observations on pigs and other domestic animals, applying their results to man. A comparative study of anatomy actively pursued during the i8th and early part of the r gth centuries, led zoologists to the discovery that all animals might be placed in a few great groups, distinguished from one another by fundamental dissimilarities in structure. Of these groups, that which attracted the greatest attention was the phylum Vertebrata. It was soon realized that all mammals resembled one another in the funda mental structure of their skeletons, that the differences that were discernible could plausibly be regarded as explicable by the loss of parts, e.g., that the hand of a horse differed from that of man by the complete loss of two outermost digits, and such reduction of the second and fourth that the third alone remained functional. Observations of this type led to the theory of "architypes" in vented by Oken, and accepted and much extended by R. Owen.
Comparative anatomy formed the foundation on which the theory of evolution was and is based. Until the community of structure which exists between animals often widely different in appearance, had been discovered, no reasons whatsoever existed for doubt of their separate creation.
Comparative anatomy forms the basis of all work on the classi fication of animals, the larger groups are established on a basis of knowledge of the complete structure of the animals included in them, and the differences which are used to separate the smaller groups, genera, and species, although they can very often be observed in surface view, are really anatomical in their nature.
The study of comparative anatomy led to the development of the conceptions underlying the terms homology and analogy, and an attempt further to discriminate between these two caused com parative anatomists to begin the study of embryology in order to determine the homologies of structures from their mode of origin. Continuation of this work and its establishment as a special dis cipline, has led to the use of the term morphology to include the old comparative anatomy, embryology and all studies in which the centre of interest is the structure rather than the function of the parts of the animal. For the further development and present position of this branch of science, see MORPHOLOGY.
(D. M. S. W.)