Architecture of the Medulla in Mammalian Vibrissae: Polymorphism and Nomenclature.

For the first time, scanning electron microscopy was used to identify, study, and systematize the architecture of the vibrissa medulla in 101 species from 80 genera belonging to eight orders of Mammalia, using an original nomenclature. A wide architectural variation is due to the diversity of sizes and relationships of vibrissal internal compartments (air cavities and partitions). Several types of the medulla were determined: membranous, pyramidal, blocky cylindrical, blocky polyhedral, chaotic, small-alveolar, large-alveolar, star-shaped, uniserial, and hollow. Different medulla types may be combined in one vibrissa. Vibrissae of a number of subterranean (moles and mole rats), semi-aquatic (desman), or aquatic (bowhead whale) species have no medulla.