school. With Aristotle (384-323 B.C.) there came a period of more exact science and the dissection of the lower animals was practised, hence Aristotle may be termed the father of Comparative Anatomy. His researches in anatomy were wide and deep and his work on animals contains much that is still taught.

The Alexandrian period, 300 B.C., during which the culture of Rome and of Greece was encouraged in Egypt under the Ptolemies, shows as a bright spot in the history of anatomical science. With the foundation of the Alexandrian Museum, the analogue of a modern university, the practice of human dissection became authorized. This period was a brilliant one in the history of medicine. Herophilus and Erasistratus were among the early leaders, the former making some noteworthy contributions to the knowledge of the anatomy of the brain. He maintained that it was the organ of thought and the origin of motion. He also described the lacteals and the lymphatics, and was an indefatigable searcher for the seat of the soul, which he placed in the floor of the fourth ventricle of the brain, the place now known to be the site of the cranial nerves, that are indispensable for the function of breathing. Herophilus also is credited with the destruction of the old doctrine that the arteries held air, hitherto the veins only having been thought to contain blood.

Erasistratus first described the valves in the veins, made the general subdivision of sensory and motor nerves, and drew the generalization of the relation of the complexity of the brain convolutions and mental development. He also first suggested the thought of anastomoses between the arteries and veins. Many others followed, but the rise of the Empirical school (q.v.) was the forerunner of the gradual decay of the Alexandrian school. It was to the newly arisen empire of Rome that the stream had turned, and until the time of Cato Greek physicians flourished in Rome. Asclepiades (126-56 B.C.) was one of the founders of the Atomic school at Rome, and Rufus (97 B.C.) of Ephesus, with A. Cornelius Celsus (25 B.C.-40 A.D.) were among those who have left definite anatomical landmarks. Celsus is known as a brilliant man, a compiler of the work of his predecessors. His anatomical work was insignificant, but he contributed largely to therapeutics. The last dying ember of this Alexandrian transplanted school showed in Claudius Galen, a Greek from Pergamos, a town already noted for its Esculapian temple. Galen was

a

man of great brilliancy, an independent thinker, and it was to his literary efforts that much of the history and treatment of the Hippocratic school has been preserved to us. His works on anatomy alone were at least 15 in number, nine of which are preserved. Galen systematized much of the anatomical knowledge of the time, and although much of his data was drawn from the study of apes it was to pass muster in the service of human anatomy. He was perhaps the first to make any experimental physiological studies. His descriptions of the relations of the brain to the spinal cord and his knowledge of the cranial nerves were in advance of his predecessors. Galen's work stands out as the last systematic work of the Greck period, and following his death began

the dark era of the barbaric inroads of the northern races and the dispersal of the culture of the East.

For a period of many centuries history is comparatively silent on the subject of medicine. No great schools arose, yet the doctrines of the ancient Greeks were kept alive in many places by obscure scholars and by many peoples, although it is known that the Saracens were largely instrumental in keeping intact that which Galen had handed down, without adding much, however, to his teachings. A flourishing intellectual development took place in the Byzantine countries, and many universities were founded by the Arabs, where the RomanHellenic culture was mingled with the Christian-Oriental ideas to found a new culture. Among the most famqus of the Oriental physicians was Sergios von Resaina (536). He translated both Galen and Hippocrates into Syrian. Oreibasios was also a commentator of the Greeks; Avicenna (980-1036) was the Galen of the Orientals. This period of medical history has been called the Arabic period, and not until the influence of the crusades commenced to make itself felt did the period of the Renaissance begin.

The history of medicine (anatomy) now becomes more and more multiplex; new schools begin to be founded. Salerno, Naples, Montpelier, Venice, Bologna, Prague, Vienna and Oxford successively built universities and attracted the ablest minds in medicine. Scholars traveled from university to university to learn from a professor here and a professor there, and the fortunes of the universities rose and fell like the tides of the sea. In 1224 it is said that the University of Bologna alone had 10,000 students. Among the early names of this period of transition may be mentioned Lisfranc (1295); Mondino (1275-1327), who wrote the first anatomy since the time of Galen, and which reached 25 editions-he also suffered persecutions for his zeal in dissecting; Linacre (1461-1524), of England, was one of the earliest scholars to bring the results of the new awakening to Oxford and to Cambridge; and Sylvius, or Jacques Dubois, a Frenchman, was another of these great early anatomists of the reconstruction period. Sylvius first arranged all of the muscles of the human body and gave them the names which, for the most part, they now carry.

Andreas Vesalius (1514-64), a Belgian, first studied at Louvain, and later became a pupil of Sylvius at Paris. At the age of 22 he became professor of anatomy at Padua, and_at 29 issued a monumental work on anatomy, the best that had been given up to that time. He corrected many of Galen's errors and had a checkered career. General gross anatomy under Vesalius, who was a son, grandson and greatgrandson of a physician, began to assume more definite_shape. In his student days at Paris under Sylvius, anatomy was taught upon the animal cadaver. Sylvius, however, was an uncompromising Galenist, and, although he made dissections, he followed Galen's treatises in very servile fashion. He was practically the last of his school, and his doctrines were swept away by the light thrown by this indefatigable seeker after truth as drawn from nature rather than from books. "My study of anatomy," said

was rapidly and superficially practised, but Vesalius is known to have haunted cemeteries and gibbets to obtain human material. The results of his studies were published in 1543 in his masterpiece, 'De Humani Corporis Fabrică. Libri VII, the first of a long series of more distinct modern treaties on physiology as well as anatomy. Vesalius may truly be said to have been the founder of modern biological science. "He brought into anatomy the new spirit of the time, the young men of the time who listened to the new voice."

Of the contemporaries of Vesalius many were almost as famous as he. Eustachius at Rome, and Fallopius at Paris, Ferrara and Padua corrected many of Vesalius's details, and Eustachius may be said to have been the first to call attention to the study of embryology as an aid in the interpretation of gross anatomy. Both Eustachius and Fallopius made noteworthy additions to the knowledge of the ear. These were the days of enthusiasm in the discovery of new facts, and so great was the striving for the new culture that it is said that criminals were utilized for purposes of experiment and dissection, probably after smothering. A large coterie of brilliant men lived at this time. Servetus (1509–53), a Spaniard, first made out many of the true facts of the pulmonary circulation. Cæsalpinus (1517-1603), a highly cultured scholar and a great botanist, was among the first to speak of the circulation of the blood. Varolius (1543-75) furthered the knowledge of the anatomy of the nervous system. Spigelius (1578-1625) made noteworthy studies of the liver. Realdo Colombo (1494-1559), who succeeded Vesalius at Padua, and was subsequently professor of anatomy at Pisa, filled out the outline of Servetus. Some authorities claim that he stole the ideas and correctly described the pulmonary circulation, although he did not appreciate the corollaries of his discovery. He imitated Vesalius and his work in a bold reproduction of his friend's studies; and Fabricius (1537-1619), who succeeded Fallopius at Padua, built a special anatomical amphitheatre where he taught anatomy to England's great anatomist Harvey.

The time had now come for a mind who could take this accumulating mass of anatomical facts, which after all were extensions in detail only of the old Hippocratic anatomy, and to discover new physiological principles, for it was noteworthy that although newer and better ideas of structure had been given, yet many of the old notions of function were still taught.

This was done by William Harvey of England. He was born in 1578, studied at many universities, mainly at Cambridge and Padua, and in 1615 first clearly demonstrated the correct action of the heart and interpreted the history of the circulation of the blood. Harvey's old anatomical preparations of this age are still in existence. From this time onward newer interpretations were possible, and the study of anatomy and physiology, now correctly linked,

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made rapid strides. These newer vantage grounds of interpretation were further extended by the discovery of the microscope, and by this instrument the field of microscopical anatomy, or Histology (q.v.), was opened up, leading to far-reaching and important results to the welfare of mankind. The period of detailed and special advance may be said to have been foretold in the newly revived study of physics by Borelli and his school, and the newer chemistry of Van Helmont won from the mysticisms of alchemy. These united to interpret the results of anatomical research, and the general history of the subject of anatomy widens out, fan-like, into its several specialties. The subject of anatomy now becomes lost in the history of interpretations and applications, and the further developments of these are considered in these volumes under their special heads where the developments of the various branches of anatomical research are considered. See ANATOMY, COMPARATIVE; ANTHROPOLOGY; BIOLOGY; CHEMICAL PHYSIOLOGY; CYTOLOGY; EMBRYOLOGY; HISTOLOGY; PATHOLOGY; PHYSIOLOGY; SURGICAL ANATOMY.

of

Bibliography.— The most extensive modern works on the history of anatomy is found with complete bibliography in Neuburger and Pagel's Handbuch der Geschichte der Medicin, (2 vols., 1903); Garrison, History of Medicine (1915); Buck, H., History of Medicine to 1800 (1917). Of descriptive anatomies there are many: Testut and Poirier in French; Bardelben and Spalteholz in German, the latter translated by Barker into English in 1903; Morris, Quain, Gray in English; Leidy, The Gerrish and Huntington in America. bibliography of the special subjects will be discussed in their sections. See MEDICINE, HIS

TORY OF.

SMITH ELY JELLIFFE.

ANATOMY, Comparative, is that subdivision of the science of zoology which deals with adult forms and structures of animals with a view to determining their relationships. Comparative Anatomy and Embryology, the latter dealing with the immature forms and structures of animals, constitute the science of Morphology, which treats of the structure, development, classification and relationships of animals as contrasted with Physiology, which Ideals with their functions. In contradistinction to special anatomy, which has for its aim the description of all the structures and parts of any one animal,- for example, man, the method of comparative anatomy is to compare corresponding parts in many different species, noting their modifications and transformations with the ultimate purpose of determining the affinities or relationships of these species to one another. In the earlier history of this science the expressions "relationship" or "affinity" were used in a metaphorical sense, signifying merely relative positions in a system of classification. With the growth of the evolution idea, however, they have acquired a new and literal meaning, since the aim of modern morphology is to determine the genetic or blood relationships of animals to one another and thereby to trace the evolution not only of the species but also of the various organs and parts. The great value of the comparative method in science is nowhere better illustrated than in the study of

anatomy. There are probably not fewer than 1,000,000 known species of animals belonging to at least 10 or 12 distinct types. These animals exhibit the various organs of animal life under a great variety of forms, and by means of comparison it is possible to determine in each case what is universal and essential and what is merely local and accidental, and also to indicate the steps by which complexity of organization has been attained. Furthermore the comparative method throws a flood of light upon the significance of problematical and rudimentary structures such as the thyroid, the thymus and pineal glands of man, the purpose of which so puzzled the earlier anatomists. In fact it may fairly be said that it is impossible to comprehend properly any structure of the human body without considering it in relation to similar structures in other animals.

I. Principles of Comparative Anatomy.It is obvious that in the study of animals various standards of comparison might be employed; for example, they might be compared as to color, size or length of life, but it is at once apparent that such comparisons would bring together animals of the most diverse characteristics in other respects. As contrasted with such a purely artificial classification it was long the aim of naturalists to find a natural system expressing the "affinity" between organisms which could frequently be better felt than described. It was the great merit of Cuvier, often called the founder of comparative anatomy, that he insisted upon the importance of comparing the totality of the internal structures as well as the external characteristics of animals. By means of such comparisons he reached the conclusion that there were four great independent branches or types of animal organization, namely, Vertebrata, Mollusca, Articulata, Radiata, each consisting of forms fundamentally like one another but unlike those of other types. The principal criterion used by Cuvier for determining this fundamental likeness or unlikeness was the relative positions of corresponding parts, particularly of the nervous system. "The type is the relative position of parts" (Von Baer). Richard Owen, a pupil of Cuvier, introduced the term homology to describe this fundamental likeness, defining it as "morphological correspondence in the relative position and connection of parts." He contrasted with this physiological correspondence of parts, which he named analogy. In closely allied animals, organs which are homologous are usually also analogous, but in less closely related ones this may or may not be the case. Organs having the same function may be structurally very unlike, for example, the wing of a bird and that of an insect; on the other hand, organs structurally similar may have very different functions, for example, the fore leg of a quadruped and the wing of a bird. This conception of homology lies at the very foundation of all morphological studies; it is the one criterion for determining likeness or unlikeness between organisms. Owen further distinguished between special and general homology, the former signifying fundamental likeness between corresponding parts of different animals, as in the case of the arm of man and the fore limb of a quadruped; while the latter refers to similar parts of the same individual, as in the case of the fore and hind limbs of a quadruped or the right and left sides of the

body. Since the term general homology as used by Owen is liable to misinterpretation it would be well to replace it by the expression meristic homology (Bateson), signifying by this term morphological correspondence between parts of the same individual which may be repeated in any relation whatever. Meristic homology would thus include correspondence between parts which are repeated in a series, for example, the vertebræ of the spinal column (serial homology, homodynamy), between parts repeated on the right and left sides of the body, for example, right and left limbs (lateral homology, homotypy) and between parts repeated in any other relations, for example, the fingers of one hand, upper and lower teeth, etc. (vertical homology, homonomy).

Significance of Homology.-To Cuvier and his followers homology meant "conformity to type," to the "archetypal plan" established by the Creator. In the light of evolution, however, homologies are believed to be family or hereditary likenesses due to inheritance from some common ancestor. For this reason special homology might better be called homogeny (Lankester) or homophyly. Contrasted with this are such morphological resemblances as are not due to inheritance, but to similarity of environment acting upon forms of dissimilar descent; such false homology is called homoplasy (Lankester), homomorphy (Gegenbaur) or convergence. It is the task of comparative anatomy to apply to animal structures these criteria of likeness or unlikeness and to distinguish between these various kinds of homology. These various forms of homology are summarized in the following table:

II. General Structures and Functions of Animals. Although the differences between the highest and the lowest animals are enormous there are nevertheless certain structures and functions which are practically the same in all animals whatsoever. All animals and plants without exception are composed of cells, while all the functions of living things are the resultants of the aggregate functions of the cells of which they are composed. The cell is thus the universal unit of organic structure and function (Cell Theory of Schleiden and Schwann), and has been defined as a mass of protoplasm enclosing a nucleus (M. Schultze). Protoplasm or living matter is a substance, usually semi-solid, of unknown but undoubtedly very complex chemical composition. It is probably composed of several complex compounds of C, H, O, and N, which do not form a mere mixture but are united in a definite and orderly way. Both the cell body and the nucleus are composed of protoplasm, though of very different quality in the two cases; that which forms the chief mass of the cell, the cell body, is called cytoplasm, while that constituting the nucleus is known as karyoplasm. At least these two kinds of protoplasm are found in every cell and are necessary to the continuance of vital activities. The cytoplasm