In this revision of his father’s anatomical treatise, Thomas Bartholin included the first depiction of the fissure of Sylvius, the lateral cerebral fissure, and the only part of the surface of the cerebral hemispheres to be given a name between 1641 and end of the 18th century when Reil described the "island of Reil" (1796; No. 1387). Sylvius (Franciscus de Le Boë) made his neurological observations in 1637 but did not publish them officially until issuing his Disputationes medicarum pars prima (Amsterdam, 1663). Sylvius collaborated with Bartholin on the above work, publishing in it ten illustrations of the brain after his own drawings.

Sylvius was a supporter of the Iatrochemical School. At Leiden he established the first university chemical laboratory in Europe. His extensive treatise on the diseases of children was first published as volume 4 of this set as De Morbis infantum et aliis quibusdam memoratu dignis affectibus. Editus cura Justi Schraderi (1674). In that work Sylvius expressed his ideas about gastro-intestinal acidity as the cause of infantile disease.

Tuberculosis was known to the ancients only in its advanced form, and little progress was made in the knowledge of the condition until the time of Sylvius. He asserted that tubercles are often to be found in the lung and that they softened and suppurated to form cavities.