472 APPENDAGES OF THE SKIN. 



of the papilla?. The Lymphatic vessels probably form, in the superficial 

 strata of the derma, a plexus, the meshes of which are interwoven with 

 those of the capillary and nervous plexus. No lymphatics have as yet 

 been discovered in the papilla?. 



The Nerves of the derma, after entering the areolae of the deeper part 

 of the corium, divide into minute fasciculi, which form a terminal plexus 

 in the upper strata of the corium. From this plexus the primitive fibres 

 pass off to their distribution, as loops, in the papillae. In the less sensitive 

 parts of the skin the loops are simple and more or less acute in their bend, 

 in conformity with the figure of the papilla. In the sensitive parts, how- 

 ever, and especially in the tactile papilla? of the pulps of the fingers, the 

 loop is convoluted to a greater or less extent, and acts as a multiplier of 

 sensation. 



APPENDAGES OF THE SKIN. 



The appendages of the skin are the nails, hairs, sebiparous glands, and 

 perspiratory glands and ducts. 



The NAILS are horny appendages of the skin, identical in formation 

 with the epiderma, of which they are a part. A nail is convex on its ex- 

 ternal surface, concave within, and implanted by means of a thin margin 

 or root in a fold of the derma (matrix), which is nearly two lines in depth, 

 and acts the part of a follicle to the nail. At the bottom of the groove of 

 the follicle are a number of filiform papilla?, which produce the margin of 

 the root, arid, by the successive formation of new cells, push the nail on- 

 wards in its growth. The concave surface of the nail is in contact with 

 the derma, and the latter is covered by papilla?, which perform the double 

 office of retaining the nail in its place, and giving it increased thickness by 

 the addition of newly-formed cells to its under surface. It is this constant 

 change occurring in the under surface of the nail, co-operating with the 

 continual reproduction taking place along the margin of the root, which 

 ensures the growth of the nail in the proper direction. The nail derives 

 a peculiarity of appearance from the disposition and form of the papillae on 

 the ungual surface of the' derma. Thus, beneath the root, and for a short 

 distance onwards towards its middle, the derma is covered by papilla? 

 which are more minute, and consequently less vascular than the papilla? 

 somewhat farther on. This patch of papilla? is bounded by a semilunar 

 line, and that part of the nail covering it being lighter in colour than the 

 rest, has been termed lunula. Beyond the lunula the papilla? are raised 

 into longitudinal plaits, which are exceedingly vascular, and give a deeper 

 tint of redness to the nail. These plait-like papilla? of the derma are well 

 calculated by their form to offer an extensive surface both for the adhesion 

 and formation of the nail. The granules and cells are developed on every 

 part of their surface, both in the grooves between the plaits and on their 

 sides, and a horny lamina is formed between each pair of plaits. When 

 the under surface of a nail is examined, these longitudinal lamina?, corre- 

 sponding with the longitudinal papilla? of the ungual portion of the derma, 

 are distintly apparent, and if the nail be forcibly detached, the lamina? may 

 be seen in the act of parting from the grooves of the papilla?. It is this 

 structure that ^ives rise to the ribbed appearance of the nail. The papil- 

 lary surface of the derma which produe.es the nail is continuous around the 

 circumference of the attached part of that organ with the derma of the sur- 



