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Rh Embryology, or development, was always neglected by Cuvier and his school, being blind to the fact that embryology must play an important part in philosophie anatomique. This fruitful field of research was left for Wolff, Vicq-d'Azyr, Von Baer, and others.

It has already been stated that comparative anatomy was the basis of Cuvier's zoology, and there are numerous and voluminous memoirs of his on the subject from 1795 to 1831—the year before his death. Among the subjects investigated may be mentioned: the structure of the larynx of birds, of the nasal fossæ and organs of hearing in the Cetacea (whales), of the organs of respiration in the perennibranchiate amphibia (in the adult state there are external branchiæ combined with lungs), the development of the teeth; and concerning the vertebrata generally he studied respiration, muscular force, animal heat, the brain and intelligence, and the digestive and nervous systems. His labours were incessant.

In 1796 he published his traité on the skeletons of the Megatherium and Megalonyx, and on the skulls of fossil bears; and between 1796 and 1812 he had examined the bones and skeletons belonging to more than forty different species. Cuvier's Xiphodon was about the size of the chamois, light, graceful, and agile, and it belonged to a tribe of animals between the Pachydermata and Ruminantia. Its fossil bones were found in the Upper Eocene strata of France. Cuvier's Palæotherium magnum