The study of intercostal muscle function began with Galen, who believed the external intercostals to be expiratory and the internal intercostals inspiratory. This teaching was unquestioned until Vesalius, thirteen hundred years later, interpreted both external and internal muscles as having the same function. Thomas Willis, of Oxford, in 1673 for the first time interpreted the external muscles as inspiratory and the internal as purely expiratory. In 1748, Hamberger devised his famous model and the theory which has been quoted in all subsequent physiologic literature on respiration. Luciani says Hamberger's model "is an incomplete reproduction of costal excursion, but it served to elucidate the mechanism"—faint praise but quite sufficient for a scheme which misrepresents both costal excursion and intercostal function.
The only experimental confirmation of Hamberger's theory that is at all worthy of the problem is Martin and Hartwell's, an account of which was published in 1879. These experimenters isolated a
HOOVER CF. THE FUNCTIONS AND INTEGRATION OF THE INTERCOSTAL MUSCLES. Arch Intern Med (Chic). 1922;30(1):1-33. doi:10.1001/archinte.1922.00110070004001