4 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS It is by means of these irregularities that the epidermis is held on to the dermis. But, in addition to this, the basement membrane sends fine projecting strands between the epithelial ceils while the latter send proto- (Slide 3) plasmic strands deep into the dermis. The dermis varies considerably in thickness in different parts of the body. It is thicker, for example, on the (Slide 4) dorsal and extensor side of extremities than on the ventral flexor surfaces. It is extremely thick on the palms of the hands and the soles of the feet. The dermis is divided into (a) a papillary layer and (b) a reticular layer. The former is composed of finer fibres and makes a sheath around the hair follicles, and the latter is composed of coarser fibres which extend into and branch among the connective tissue of the sub-dermis. In some parts :: ' ..... ' .: ".i '%•.. ":•:':'"' ...•!•:•:.-•? -½•. ß (...5•. •,'-•. •:.,:.. ...... -.-.& • ... .... •y•. ....: •:...• •: ' .:.. ....... ........ •::• ' ' :'3 •-•' :'•i ' '" - ---. '--' ½}-:½'• 5• "2' ...d• ' v .::. /•..•.,.::.•%., • •.. ,½ ...• -. :.:..... ,-...•:.:..... . ....... ß ...... •..:? ß . ..7 'x• .... • .... ß ½ .i:-..y :- x..:. .... •.. - :2.. ß ...... ,+. ß ß • ... .:..: •.'.' ...}. :½• '. '. •.,•. ,.:: :.::-:...• . •} ß : 'r.' .'•:. :.. '•:•:, '• .•. :.:....., ....,.--•.: ß .:,•-½.•::•.,.,. ..::....:.-.:: :-. •-•, . ... ..... . ...... . ..... .... : - . . 4 ::. -..• (,• . -... . [ .• ß '"'.:.:.•¾:.".•,• ::: ½'.:5:. . " ??' -.... "• ' '"" '""'"':: ':'""•:• •:' .: ,.,- ,•. --- :.? •:'•::'•: •&-. :,.• • .•:,. . •:.: .•:½• :,:' •:: .'•.:.:,..::: ,.½s• .... --,:.-:.•..: -- ..... }•:5•.'½• ½'.: SLIDE 3 Epidermis of the palm showing the delicate cytoplasmic processes at the base of the stratum germinativum. This section was treated with the technique of Barrnett and Selig- man (19) for the demonstration of disulfide groups.

THE STRUCTURE OF SKIN 5 of the body the dermis contains smooth muscle fibres. These may be found in the skin round the nipple, the penis and the scrotum. BLOOD SUPPLY TO THE SKIN In the deep connective tissue underlying the epidermis small arteries form a rich arterial plexus. From this plexus arterioles pass more or less perpendicularly upwards to form the sub-papillary plexus from which smaller vessels, the terminal arterioles, supply the papillary capillaries. (Slide 5) The illustrations demonstrate the arrangement of the vessels. The terminal arterioles and the metarterioles have smooth muscle in their SLIDE 4 The basement membrane of the epidermis from the scalp. The "membrane" is actually a complex argyrophilic network through the meshes of which protrude the cytoplasmic processes of the basal cells. This section was treated with Gomori's ammoniacal silver nitrate technique.