THE SKIN 1283 



placed by whitish, silvery lines, striae or linese albicantes, due to atrophy of the tissues. In 

 spite of this the skin usually retains enough elasticity to contract gradually to its former 

 extent as it does immediately after moderate stretching. 



In most parts of the body the attachment is loose so that the skin is movable and may be 

 pinched up into folds. In some places the attachment of the skin is firm and there is no slip- 

 ping of the skin over imderlying parts, as on the glans penis. In some other parts the motion 

 is very limited as in the scalp and the volar surface of the hands and the plantar surface of the 

 feet. 



Fig. 1042. — Finger Print (Natural Size) Showing Crist.e and Sulci. 



Sulci 



Cristae 



^^^M^^ Longitudinal 





The colour of the skin varies greatly. It may be white, yellow, black, red, or 

 any of the shades of these colours, and, according to the colour, the races of man- 

 kind have been roughly divided. The colouration is due partly to pigment and 

 partly to the blood within the cutaneous vessels. The amount of pigment varies 

 with race, age, sex, and with exposure to the sun and air. In the white races the 

 skin of the child is a pinldsh white, tending to become dead white in the adult 

 and yellowish in the aged, and it is normally more pigmented in certain regions, 

 such as the axillary region, the scrotum, the vulva, and the mammary areola. 



Fig. 104.3. — Diagr.\m Showing the Arrangement or the Principal Crist.e of the Thumb 



The colour of the white, yellow, red, and black races is not produced by the climate, as we 

 find different races existing under the same climatic conditions and the same coloured race under 

 different conditions of chmate. Each race presents several variations of colour; for example, 

 in the white race we distinguish a blonde, a brunette, and an intermediate type. Anthropolo- 

 gists distinguish twenty to thirty different shades of colour in the skin. In blondes of the white 

 race vmder the action of strong sun light the skin passes from a rose white to a brick red or 

 becomes pigmented in spots, freckles. In the first case the pigment in the skin is not increased 

 to any great e.xtent but the skin is affected by a superficial inflammation, erythema, associated 

 with exfoliation and often with the formation of blisters. In brunettes of the white race the sun 

 bums the skin a dark yellowish or reddish brown, the degree of pigmentation here being increased 

 and is spoken of as tan. The colouration is only temporary and diminishes on withdrawal from 

 exposure. The sim darkens the skin in the yellow races also. In the newborn of the black 

 races the skin is of a reddish colour, since the pigment although developed to some extent is at 

 birth obscured by overlying opaque cells which later become transparent. The newborn of the 

 yellow races are also lighter than their parents. In white races the shade of the skin is clearer on 

 the ventral surface of the trunk and on the flexor surface of the extremities. In the black races 

 the volar surface of the hands and the plantar surface of the feet as well as the sides of the digits 

 are less deeply pigmented than the rest of the body. The colour of the skin is greatly influenced 

 by the blood in its deeper layers which during hfe gives it a more or less distinctly reddish tinge, 

 varying directly with the vascularity and inversely with the thickness of the epidermis. Absence 



