THE SKIN 



Bv WILLIAM ANDERSON, F.R.C.S. 



SURGEON TO AND LECTURER ON ANATOMY AT ST. THOMAS'S HOSPITAL; PROFESSOR OF ANATOMY IN TUE ROYAL 



ACADEMY ; EXAMINER IN SURGERY AT THE UNIVERSITY OF LONDON AND ROYAL 



COLLEGE OF SURGEONS OF ENGLAND 



The skin is a niemhranous investment forming the entire external surface of tlie 

 body and its memliers, and is continuous at certain points with the internal lining 

 of the alimentary, respiratory, and urinogenital canals. 



Its extent has been estimated at al)OUt 15,0(X) square cm. in an adult malf of 

 medium size (.Sappey). In thickness it varies considerably in different ]K)rtioiis of 

 the surface, ranging from -V to tV ^^ ^^i inch (0-5 to 2 nnn. ), but ap])ears to be pro- 

 portionate to the amount of pressure or friction to which the parts are habitually 

 subjected. Thus it is thickest ui)(m the nape, back, and shoulders, and on the 

 palms and soles, while on the front of the trunk and on the dorsal as]X'ct of tlie 

 hands and feet it is relatively thin. It is highly elastic and is capable of stretch- 

 ing to a considerable extent without rui)ture of its continuity, and of regaining 

 its original condition when the extending force is removed. This quality is es]H'- 

 cially remarkal)le in the distension of the integuments over a slow-growing 

 tumour. Its colonr is due partly to pigmentation, partly to the blood within its 

 vessels. The amount of ])igment varies with race, sex, age, and with ex])0sure to 

 sun and air; and is normally greater in certain portions of tlie skin (axilla, scrotum, 

 vulva, mammary areola", etc. ) than on the rest of the sm-face, besides Iteing subject 

 to ]>hysiological and pathological variations. Its surface is for the most jiart 

 smooth, but is diversitied l)v the orifices of glands, by the growth of hair, and bv 

 various furrows and elevations. Permanent linear ridges are present upon the 

 palms and soles, and flexor surfaces of the digits; and tem])orarv pa])ular elevations 

 (' goose-rtesh ' ) may appear in the positions of the hair-foil iele<s under the inthi- 

 ences of cold or emotion. The ])ermanent ridges, corresponding to rows of dermic 

 papilla', have an arrangement of a pecidiar kind over the front of the terminal 

 joints of the lingers, and their variations liave been classified in such a manner as to 

 prove valuable for ])in"posesof identiMc;iti<)n. In jirimitive races the inqirint of the 

 thumb has hern usc(l as a kimi of signature. 



Tile furrows or depressions are of several kinds. The most jiermanent are 

 those which separate the i)apillary ridges on the]>alni. IJelaxed ])ortionsof theskin, 

 such as that of the back of the hand during extension of the wrist and fingers, are 

 crossed by a multitude of tine decussating wrinkles, which disajtpcar when the sur- 

 face is stretched; other lines of a more constant type are produced l)y joint flexion, 

 such as thovse in front of the wrist; others are caused by contraction (»f voluntary 

 or involuntary muscles, such as the lines of exjiression on the forehead space, the 

 transverse wrinkles on the scrotum, and the radiating folds around the anus, the 

 lines then running at right angles to the direction of the muscular fibres by which 

 they are produced; lastly, a complex wrinkHng of the skin appears in old age or in 

 the course of exiiausting disease.««\ partly as a result of lo.«s of elasticity of the 

 structures and partly from altsorjition of the cutaneous and subcutaneous fat. 



In addition to these linear depressions are more rotuxled forms, called dimples, 

 68 1(>7"; 



