.STRUCTURE OF THE SKIX 1075 



definitL' plan. Lantror and otliers have shown that if the skin is jiuiKtun-d hy an 

 awl, tlie ai)ertur(,' k'ft on \vitli(h-a\vin<; thi- inijili iiicnt is not roinid, hut Hnear or 

 angular. On the scalj), forclu-ad, cliin, and I'pigastriuni a trianguhir or raggcfl hole 

 is produced, while over the rest of tiie hcxly the ' cleavage ' is linear, the lines 

 affecting a direction nearly at right angles to the long axis of the limbs, and on the 

 trunk running ol^licjuely downwards, and outwards from the H\nnv. The linear 

 cleavage indicates that tlie bundles run mainly in one directi(»n, while the 'incom- 

 plete' cleavage is associated with a crossing in all directions. Tiie arrangement of 

 the vessels of the skin is said to l»e governed by the cleavage, and tiie form and 

 distril>ution of certain skin erui)tioiis are ])robabiy connected witli these factors. 



The papillae are very closely set — from 'My to i;50. according to Sai»]»ev, lying 

 within a square millimetre. The largest are found in the palm and sole and under 

 the nail, reaching a heiglit of half a line or a line (1 to 2 nnn. ); the smallest, 

 distributed over the face, scrotum, and mamniilhr, having only a third or a fourth 

 of these dimensions. The forms usually assumed are those of sim])le cones, but 

 some are slightly l)ull)Ous at their free extremities; others have dujilicated apices, 

 and those about the i)almar and plantar surfaces of the hands and feet form long 

 curvilinear ridges, which are pierced ])y the orifices of the sweat ducts, and separated 

 from each other l)y furrows. It is only in these latter situations that the arrange- 

 ment of the papillie is unconcealed by tlu' e])idermis. Structurally, the pajiilla 

 consists of a delicate lil)rous tissue containing vessels and nerves, or, in certain 

 situations, a special tactile body. Its sul)e])idermic surface and that of the inter- 

 ]iapillary depressions is modified into a delicate, structureless lamina, called the 

 membrana basilaris. 



The epiderm, or cuticle, is a layer of varying dci)th, the tliickness being regu- 

 lated chiefiy by the amount of i)ressure or friction to which the ])art is habitually 

 suV)jected. Its deep aspect is moulded to the papillary layer of the derm, while its 

 free surface gives little or no indication of the ])ai)illarv eminences except f)n the 

 palms and soles, l)ut it displays numl)erless apertures of glands and hair-follicles, 

 which it lines with tubular prolongations. Structurally, it consists entirely of e]ii- 

 thelial cells of various shajx'S. The component cells may l)e divide(l into five distinct 

 layers, arranged from within outwards in the following order: (1) The stratum 

 basilare, or generative layer, consists of a single set of nucleated, ]»rismatic cells, the 

 denticulated bases of which rest upon the l)asement membrane of the derm. (2) 

 The stratum Malpighii, succeeding this, is a soft, relatively tliick layer, com])osed of 

 several ranges of nucleated cells, i)olyhedral in shape, denticulated on all sides, and 

 separated from each other liy fine intercellular channels, in which may be lym]»h 

 corpuscles- and even pigment. The cells are tlie sent of tlic i.ignicnt granules which 

 give to the .skin a portion of its colour. (3) The stratum granulosum coiniirises 

 two or three layers of transitional cells, resembling tiiose of the stratum Malpighii 

 in the denticulation of their oj)posed sides, but fiattened in the direction of the 

 surface and containing a number of minute granules, which readily take the stain 

 of carmine or logwood, and are coni]H»sed of a jx'culiar substance, called eleidin, 

 or kerato-hyalin, that is said to be the active agent in the keratinic transformation 

 of the more superficial cells, and is, perhaps, to be regarded as the earliest ])roduct of 

 the retrograde change which ends in keratinisation. (4) The overlying layer, the 

 stratum lucidum of Ochl, represents the first stage of the homy change. It is 

 seen in sections of the skin as a transparent liand, which on close examination is 

 fi»und to be made up of colourless cells with indistinct marginal denticulation and 

 atrophic nuclei, and fiattcncd in the direction of the surface, (o) The sui)erficial' 

 layer, the stratum corneum, is not very sharply define(l from the last, and shows 

 a further advance in the horny degeneration, if such a term may be apjilied to a 

 jiurposcful and necessary change. The cells are highly keratini.sed. and ajiju-ar as 

 thin, transparent scales, from ■which both denticulation and nuclcatioii have dis- 

 appeared, the latter, however, still Ixing traceable after macerati<^n in dilute 

 alkalies. 



The life history of theejiiilennis appears to be that of a c<intinuous genesis, from 

 the stratum basilare. of new cells which rise slowly towanls tlie surface to a.<sume 

 in succession the characters of the cells in the older stratmn above, nud l»ecome in 

 turn replaced l)y their successors from below, until, having ].assed through all tlie 



