APPENDAGES OF THE SKLV 1077 



THE APPENDAGES OF THE SKIN 



Under this heading are included sudoriparous and sebaceous glands, hair, and 

 nails. The sudoriparous glands, wliich secrete the sweat, and pn.l.al.ly a certain 

 amount of oilv matter in addition, have their origin in a single coiled tui.e, which 

 forms a spheroidal glomerulus in the deeper i)art of the derm, or even in the suhcu- 

 taneous tissue, and is continued into an excretory duct that jjierces tlie interi)apillary 

 spaces of the derm, and traverses tlie epiderm in a sinuous or sjiiral course to oj)en 

 on the surface. They are most numerous on the jialms and soles, least so on the 

 Iiack of the neck and' trunk and on the lower limbs. Sai)i)ev estimates the total 

 number over the whole body at 2,000,000. The glomeruli 'range from one two- 

 hundred and fiftieth of an inch (O'l mm.) to a line (2 mm.) in diameter, and are 

 largest in the axilla and groin and about the mannnary areola. The tube wall 

 consists of an epithelial layer of })rismatic nucleated cells, sup])orted ])artly by an 

 incom])lete layer of cells, l)elieved to be those of unstrij)ed muscular til)re, ])arily 

 by a structureless membrana proi)ria lying outside; the last and continuous with the 

 basement membrane of tlie <lerm. The 'nmscidar' layer is ab.-cnt in the excre- 

 tory duct. Allied to the sudorii)arous glands are the ceruminous glands of the 

 external auditory meatus, which have the same structure, l)ut jjrimitively open into 

 the hair-follicles; and the ciliary glands of Moll, opening on the free border of 

 the lids, which do not form glomeruli. 



The sebaceous glands are found over the whole area of the skin except on 

 the palms and soles. They difter from the sudoriparous glands in their racemose 

 form, in their almo.st constant relation to the hairs, in the oily nature of their 

 secretion, and in their com})aratively su])erficial j)osition. The greater number 

 discharge their contents into the hair- follicles, one, two, or more Iteing attached to 

 each hair; others open directly on to the surface, and either present a rudimentary 

 hair emerging from the excretory duct or are altogether unconnected with hairs, 

 as in the labia minora and mammary areola. It is these last which attain the 

 greatest size. Their acini are invested by bands of unstriped muscles which aid in 

 the exjiulsion of their contents, and in the case of the larger hairs act as ' arrectores 

 pilorum.' 



The nails are essentially an epidermic specialisation. Rudimentary in man, 

 they are largely developed in many of the lower animals, taking the form of claws 

 or hoofs. In man the nail ajjpears as a horny ]»late on the dorsal aspect of tlie 

 terminal ])halanx of the digit; it is straight, or nearly so, in its longitudinal axis, 

 but curved in the opposite direction, with the convexity outwards. The entire nail 

 is divided into a root, thin, soft, and buried in a fold of skin; a body, hard and 

 keratinised, longitudinally ri<lged on its dorsal aspect, and extending from the 

 root to the line at which the ai)pendage ceases to be connected with the skin; and 

 a free extremity, which, unless restrained by artificial means, tends to grow into' 

 a claw-like form and may curve over strongly towards the pahiiar surface of tlu- 

 diiiit. The point at which this joins the i>ulp of the finger is called the angle. 



The colour of the nail varies in its different i)arts. The greater i)art of tlie body 

 has ai>inkish tint which may l)e expelled In' pressure, and deitends u}>onthe vessels 

 lieneath; Imt near the root is a white crescent, the lunula, most largely developed 

 on the thumb, least on the little finger, where it is often concealed liy the overlajv 

 ping border. The free extremity is semitransparent and almost colourless. 



The surface of the nail, especially that of the thumb, may under certain <ir- 

 cumstances present transverse furrows and ridges corres]ion<ling to irregularities of 

 nutrition; and as the growth of the entire length of tlie nail occujjies on the average 

 about six months, it is sometimes ])ossible to surmise roughly, by an ungual 

 inspection, the jdiysical history of the person within that ])eriod. 



Hairs. — Man, like the rest of the mammalia, is a hairy animal, but the greater 

 part of his hirsute covering assumes the form of a scarcely visil>le down. It attains 

 a considerable develojtment only in certain regions, and it is lacking on tlie llexor 

 surface of the hands ami feet ami their digits, on the back of the terminal phalanges, 

 and at certain rellections of the integument, as the )>re]>uce and glans penis, the 

 inner aspect of the labia majora an<l the labia minora. The distril>ution of larger 



