A scanning electron microscope study of the morphology of rhinoceros horn.

The morphology of rhinoceros horn as revealed by the scanning electron microscope is reported. The results are broadly consistent with previous studies of the material. Two different-shaped cortical cell units are shown to exist. The more numerous scale-like cells form the concentric laminae which are packed around the central non-fibrous cores of fibrillar units which comprise most of the horn structure. Regions of interfibrillar material are shown to exist and it is possible that the minority cells originate from it. (1) The horn is composed of tubular or filamentous units 300-500 (Lm in diameter. (2) These units are closely packed and as a consequence are distorted from a cylindrical shape. (3) Interfilamentous horn is concentrated mainly, if not only, at the inter-stices rather than between the flat surfaces between the filaments. (4) The filaments are composed of about 40 laminae arranged concentrically around a medulla which is a "clearly demarcated solid structure that has either several small gas spaces, or one large irregular one occupying almost the whole width of the medulla" (Ryder 1962). (5) The laminae are sheets composed of a single layer of flat cortical cells. We have studied the morphology of the horn of an African white rhinoceros (Cerathotherium simus) by scanning electron microscopy. Two instruments were used-a JSM2 and a Cambridge Stereoscan Mk.IJ. Both cut and sheared longitudinal and transverse surfaces were observed and also surfaces formed by snapping after immersion of the horn in liquid nitrogen. After preparation some specimens were soaked in water and then dried at lO5°C. Material swollen in formic acid was also studied together with the product of disintegration in heated formic acid.