Page:Encyclopædia Britannica, first edition - Volume I, A-B.pdf/302

 2 $6 Part VI. ANATOMY. is the membrana adipofa, or corpus adipofum. This is After this femilunar fold, the Ikin is continued on the not, however, a Tingle membrane, but'a congeries of a whole inner furface of the nail. The fold of the Ikin is great number of membranous laminae, joined irregularly accompanied by the epidermis, to the root of the nail to each other at different diltances, fo as to form numeto which it adheres very clofely. rous interftices of different capacities, which communicate exteriorly, parts are generally diftinguilhed in the nail, the with each other. Thefe interftices have been named cel- root,Three body, and extremity. The root is white and in lulx, and the fubftance made up of them, the cellulous form of a crefcent; and the greateft part of it is hid unfubfiance. der the femilunar fold already mentioned. The thicknefs of the membrana adipofa is not the The crefcent and the fold lie in contrary direftions to fame all over the body, and depends on the number of each other. The body of the nail is naturally arched, laminae of which it is made up. It adheres very clofe- tranfparent, and appears of the colour of the cutaneous ly to the Ikin, runs in between the mufcles in general, papillae which lie under it. and between their feveral fibres in- particular, and com- The principal ufe of the nails is to ftrengthen the ends municates with the membrane which lines the infide of the of the fingers and toes, and to hinder them from being thorax and abdomen. towards the convex fide of the hand or foot, The ftrufture is demonftrated every day by butchers, inverted when we handle or prefs upon any thing hard. in blowing up their meat, when newly killed; in doing which, they not only fwell the membrana adipofa, but THE HAIRS. the air infinuates itfelf likewife in the interftices of the mufcles, and penetrates even to the vifcera, producing a The hairs belong as much to the integuments as the kind of artificial emphyfema. nails. They are a kind of reeds or rulhes, the roots or Thefe cellular interftices are fo many little bags or bulbs of which lie toward that fide of the Ikin which is fatchels, filled with an undtuous or oily juice, more or next the membrana adipofa. The trunk or beginning of lefs liquid, which is called fat. the Item perforates the Ikin, and the reft of the Item adThis fubftance increafes in quantity in the body, by vances beyond the outer furface of the Ikin, to a certain reft and good living; and on the contrary, diminilhes by diftance, which is very various in the different parts of the body. hard labour and a fpare diet. The proportional differences in the thicknefs of this When the different hairs are examined by a micromembrana adipofa, are determined, and may be obferved fcope, we find the roots more or lefs oval, the largeft to be regular in fome parts of the body, where either extremity being either turned toward, or fixed in the beauty or ufe required it. corpus adipofum. Thus we find it in great quantities, where the inter- This oval root is covered by a whitilh ftrong membrane, ftices of the mufcles would otherwife have left difagree- in fome meafure elaftic; and it is conneifted either to the able hollow or void places; but being filled, and as it Hein, to the corpus adipofum, or to both, by a great ■were padded with fat, the ikin is raifed, and an agree- number of very fine veflels and nervous filaments. Within the root, we obferve a kind of glue, fome able form given to the part. In fome parts of the body the fat ferves for a cufhion, very fine filaments of which advance toward the fmall pillow, or mattrefs ; as on the buttocks, where the lami- extremity, where they unite and form the ftem, which paffes through this final! extremity to the Ikin. As the; nae and cells are very numerous. The fat is likewife of great ufe to the mufcles, in pre- ftem paffes through the root, the outer membrane ' s ferving the flexibility neceffary for their aftions, and in elongated in form of a tube, which clofely invefts the ftem, and is entirely united to it. preventing or leffening their mutual fridtions. The ftem having reached the furface of the Ikin, pierces the bottom of a fmall foflula between the papilTHE NAILS. lae, or fometimes a particular papilla, and there it meets The fubftance of the nails is like that of horn, and the epidermis, which feems to be inverted round it, and they are compofed of feveral planes of longitudinal fibres to unite with it entirely. A fort of umftuous matter foddered together. Thefe ftrata end'at the extremity of tranfudes through the fides of the foffula, which is beeach finger, and are all nearly of an equal thicknefs, but llowed on the ftem, and accompanies it, more or iefs, as it runs out from the Ikin, in form of an hair. of different lengths. The external plane or ftratum is the longeft, and the reft decreaie gradually, the innermoft being the ftiorteft; Sect. II. Of the Abdomen. fo that the nail increafes in thicknefs from its union with the epidermis, where it is thinneft, to the end of the fin? The Abdomen begins immediately under the thorax, ger, where it is thickeft. the bottom of the pelvis of the offa inThe graduated extremities or roots of all the fibres of and terminatesItsatcircumference, or outer furface, is diwhich thefe planes confift, are hollowed for the reception nominata. into regions, of which there are three anterior, of the fame number of very fmall oblique papillse, which vided the epigaftric or fuperior region, the umbilical or are continuations of the true Ikin, which having reached viz. middle region, and the hypogaftric or lower region. to the root of the nail, forms a femilunar fold, in which There is but one pofterior region, named regio lumbaris. that root is lodged.