Still under the hallucination caused by the Galenical theories, anatomists thought that both lacteals and thoracic duct could be traced to the liver. Rudbeck discovered the general lym phatics in 1651.
A clearer idea of the gross anatomy of the brain, especially of its internal cavities, was due to the descriptions of Francis Bo6, usually known as Franciscus Sylvius (1614-72), pro fessor at Leyden, whose name survives in the aqueduct, fissure, fossa, and artery of Sylvius. The science of chemistry was at this time grad ually emerging from the superstitions of al chemy. and Sylvius is also famous for being among the first to attempt to differentiate the structures and fluids of the body by means of their chemical reactions. Vieusscns (1641-1715) of Montpellier also increased the knowledge of the nervous system, both central and peripheral, describing the anterior pyramids, the olive, and the anterior medullary velum which sometimes bears his name. To Thomas Willis (1622-75) (q.v.) of London. sometime professor at Oxford, is due a systematic description of the brain and its cavities, together with a classification of the cranial nerves in which he finally separated the sympathetic cord from that series. He rec ognized that the brain becomes gradually more complicated as we ascend the animal scale, and that it is more easily understood by a study of the lower and more simple forms. The decussa tion of the pyramids was first described by Duverney (1648-70), demonstrator at the Jar din du Roi, afterward the Jardin des Plantes. at Paris. The doctrine of the "animal spirits," supposed to fill the ventricles of the brain and to be distributed by the nerves, was first seri ously attacked by Wepfl'er (1658).
The advance of the physical sciences insti tuted by Galileo (1564-1642) had a profound effect upon anatomy. The new developments in optics were now called on to contribute to the problems of structure. The optical prop erties of the crystalline lens were now described by Kepler (1571-1630) (q.v.). the eminent as tronomer, who denied that it is the seat of vision as supposed by Hippocrates; the image on the retina was demonstrated by Scheirer (1575-1050) ; Descartes (1596-1650) showed the eye to be a camera obseura, and suggested that accommodation is produced by a change in the convexity of the lens. Ile also made some
very acute observations on the structure and functions of the nervous system.marred, however, by metaphysical speculations that were attacked by Stensen, who declared that in order to deter mine the functions of organs we must first ascer tain their structure.
A new instrument of research which the Ital ians, impelled by the zeal imparted by Galileo, were the first to apply to scientific uses. was now introduced. This was the microscope, hitherto merely an optical curiosity. The magnifying power of convex lenses was known to the an cients, for even in the ruins of Nineveh a pol ished rock crystal lens has been found, and there is good reason to believe that similar instruments were used in ancient Egypt and in Greece. Spectacles were used in Europe as early as the thirteenth century, and the compound mi croscope was invented about 1590 by Hans and Zacharias Janssen of Niddelburg, Holland. No means for correcting chromatie and spherical aberration being then known, the first instru meats were clumsy and imperfect; consequently, many investigators preferred to use the simple microscope, especially after Leenwenhoek had shown what excellent results could be obtained with small but accurate lenses.
Among the first and most acute observers was Mareello Malpighi (1628-94), professor at Bo logna, Pisa, and Messina, a man of extraordinary acuteness of intellect, combined with an indom itable zeal for natural research. He left his mark in almost all departments of biology. He was an accomplished botanist, and by his re searches among plants laid the foundations of the modern cell-theory; he was an entomologist, devoting himself to an exhaustive study of the anatomy and development of the silk-worm; he was an embryologist, being the first to build upon the incomplete studies of Harvey and Fab Heins and describe adequately the changes of the chick in the egg; lie was a pathologist, studying carefully post - mortem appearances and the causes of disease; he was also a compar ative anatomist, drawing many of his conclu sions as to the structure of man from an exam ination of animals.