1152 



THE ORGANS OF SPECIAL SENSE 



RIDGES OF 

 SKIN 



FURROWS 

 OF SKIN 



FLEXION FURROWS 

 OPPOSITE THE 

 FLEXURE OF 

 THE JOINT 



touch (organon tactus). These nerve terminations are connected with nerve 

 fibres of temperature, pressure, and pain. Connected with the skin are sweat 

 glands which have important excretory functions and sebaceous glands. From 

 its superficial part come appendages, the hairs, and nails. The skin is elastic 

 and varies in thickness from 0.5 mm. to 4 mm. (-^ to ^ inch). It is thinnest 

 in the eyelids and prepuce, and thickest over the back of the neck, back of the 

 shoulders, palms of the hands, and soles of the feet. Its color depends in part 

 on the blood within it, and in part upon pigment. The deepest hue is about the 

 anus, in the genital region, in the axillae, over the mammary glands, and in the 

 parts exposed to air, light, and varied temperatures. The color varies with age, 

 being pinkish in extreme youth and becoming yellow in old age. It varies with 



exposure and with climate, being 

 deepest in those who brave all 

 weathers and temperatures and in 

 those who dwell beneath a tropical 

 sun. It also varies with race, and 

 this is so well recognized that races 

 are classified by the color of the 

 skin into the Black, White, Yellow, 

 and Brown races. The color of the 

 skin is also affected in certain dis- 

 eases; being extremely pale in 

 anemia, brown in Addison's disease, 

 yellow in jaundice, etc. 



In most situations the skin is mov- 

 able, but in some it is attached closely 

 to underlying structures, and is con- 

 sequently immovable on the scalp, 

 the palms of the hands, the soles of 

 the feet, and the outer portion of the 

 pinna of the ear. The skin is fairly 

 smooth, but close examination dis- 

 closes multitudes of openings, creases, furrows, depressions, folds, and hairs. 

 Hair follicles open upon the surface, and the ducts of sebaceous glands and of 

 sweat glands perforate the skin. 



About the joints are folds of skin (retinacula cutis), and temporary folds or 

 wrinkles are created by the contraction of superficial muscles. The facial wrinkles 

 of advancing years are due to habitual expression and loss of skin elasticity. A 

 dimple is a permanent pit or depression due to adhesion of the surface to parts 

 beneath. The ridges and furrows on the palms, soles, and flexor aspects of the 

 digits are permanent, and over the palmar surface of the digits they are arranged 

 in definite forms which endure through life and are so distinctive that they have 

 been utilized by police officials in determining the identity of individuals. These 

 folds are due to the papillae of the skin being arranged in rows ; some of the papillae 

 proliferate, and linear depressions occur in the horny layer (Philippson). 



Fig. 861 shows skin ridges (cristae cutis), skin furrows (sulci cwfr'*), furrows 

 opposite joints due to acts of flexion, and called flexure furrows, and longitudinal 

 furrows. 



^ When the skin is punctured by a round awl it tends to split in a definite direc- 

 tion, which direction varies with the region stabbed. These clefts are known 

 as the cleavage lines of Langer (Figs. 862 and 863), and depend upon the arrange- 

 ment of the connective-tissue bundles of the corium. These connective-tissue 

 bundles certainly influence the formation of folds and furrows. In many portions 

 of the body the cutaneous surface is divided by linear furrows into irregularly 



LONGITUDINAL 

 FURROWS 



FUDGES OF SKIN 



INTERRUPTED BY. 



LONGITUDINAL' 



FURROWS 



FIG. 861. The furrows and ridges of the surface of 

 the skin from the palm or surface of the middle fineer 

 (Toldt.) 



