Dermatoglyphics on volar skin of mice: the normal pattern

Mouse volar skin has many protrusions, both large and small. They can be observed more clearly after removal of the epidermis, as they are chiefly constructed of dermal structures. They form "dermatoglyphs." This report describes the normal pattern of these protrusions to establish a normal standard for detection of abnormalities.

Limbs of young and adult mice were fixed in 10% formalin and treated with 5% KOH to remove the epidermis layer. They were observed under a dissecting microscope after toluidine blue staining, or by scanning electron microscopy. Several limbs were used for light microscopic observation.

Four types of protrusions are observed. 1) Digital pads: single large pads on each digital tip. They locate over the distal phalanx. 2) Interdigital pads and carpal (tarsal) pads (or thenar and hypothenar pads): large pads similar to digital pads. There are five on the palm and six on the sole. 3) Caterpillar pads: elongated thin protrusions on the ventral side of the digits. They form stripes transverse to the axis of the digits. 4) Cobblestone pads: many small protrusions between the interdigital and carpal (tarsal) pads. "Caterpillar pads" and "cobblestone pads" are reported here for the first time. Each pad contains sweat glands and has sweat duct openings and dermal ridges on its top.

A detailed description of the normal pattern is indispensable for identification of abnormal patterns. The present description, therefore, can be used as a normal standard when genetically or environmentally induced anomalies are assessed.