Ultrastructural study of the medulla of mammalian hairs.

Coordinated studies with the SEM and CTEM have allowed the authors to observe in situ the morphology and ultrastructure of about twenty different types of hair selected on the basis of their different characteristics when studied by optical microscopy. The new data thus obtained make it possible to classify the different types of hairs in a logical order (parallel to Hausman's classification). The classification is based on the fine morphology and the ultrastructure of the medulla and the differences encountered in the main mammalian orders. Furthermore the chronology of these characteristics follows that of mammalian phylogenesis. The ultrastructural characteristics of the medullar of human hair are totally different from those of the hair of all other mammals.