INTEGUMENTS. 



to tlie nail, there would be a fpecies of cul-dc-rac between 

 thefe parts. Some have conceived that the extenfor tendon 

 reaches to the pollcrior edge ; but its termination at the 

 tubercle of ihe lad phalanx is very diftinft ; and there is a 

 fpace of two or three lines between this and the nail. The 

 concave furface of this pcilerior divifion adheres in the fame 

 way as that of the middle part. 



The convex unconnefted furfsce of the middle divifion is 

 fmootb, whitifh behind for a fii;all fpace terminated by a 

 femicircular edge, and red in the reft of its extent in con- 

 fequcnce of the colour of the fubjacent parts. On the 

 fides it is covered a little by the ilvin, wliich is continuous with 

 the feniil'.inar projedlion already defcribed. The fold of 

 cuticle is alfo continued, and adheres to the margin of the 

 nail. The concave furface of this part is laminated longi- 

 tudinally, and the plates end in very »h;n and mer.ibrane-Uke 

 edges ; but this laminated texture does not extend to the 

 white part. The organization may be well Icen in the hoof 

 of an animal, as the horfe ; Vi-here the plates are of coiifi- 

 derable breadth and number. 



The edge of this concave adliering portion is fixed in 

 front by the epidermis, which, after covering the extremity 

 of the finger, is attached to the furface of the nail at the 

 front end of its laminated portion, in a curved line ; here 

 ag-.iin it feems to be confounded v.-ith the fubilance of the 

 oaii. 



The loofe anterior portion, the length of which is limited 

 by cutting, is manifeilly thicker than the middle and pollerior 

 parts. Indeed the thickncfs, hardnefs, and refillance of the 

 organ increafe gradually from behind forwards. 



At the attachment of the nail, the f]<in is m?,rked by a 

 deep parabolical groove, in which the former is received : 

 the fold, which bounds this groove behind, overlaps the 

 white part of the nail, covers a confiderable portion of it, 

 and adheres firmly to the pofterior thin edge. From' this 

 hollow the cutis is produced over the pollerior furface of 

 the lail phalanx to the end of the finger, between the nail 

 ahd the bone, and adheres clofcly to the periofleum. At 

 the fides and in front it is continuous with the common 

 {Tcin. In this fitu^.tion it has a peculiar organization ; it 

 becomes fofter and redder, has more numerous veffels, and 

 is diftributed in longitudinal lamin.T, correfponding to, and 

 received between, thofe of the nail. Bat the portion of 

 ficin correfponding to the white part of the nail, is' alfo 

 different in its colour, and not laminated on its furface. 

 From this part numerous fine and long papillx or villi arife, 

 and are received into correfponding hollows of the nail : 

 the fame ftrufture exills more or lefs over the whole furface 

 covered by the nail. It appears that the organ grows prin- 

 cipally from the white part : at leall, if a mark be made 

 towards the root, it gradually advances to the loofe edge, 

 coming more and more forwards until it entirely difappears. 

 The papills of this part give to the organ a very exquifite 

 fenfibility : hence the acute pain of paronychia, and of that 

 b'arbarous praflice of tearir.g oft" the nails. 



Organ'izdlioa and Properties of the Nails. — ^Thefe can be 

 inoft advantageoufiy obferved in the larger ones, as thofe 

 of the thumb or great toe. A fingle lamina occupies the 

 whole convex furface ; this exills alone at the pofterior edge, 

 and hence the thinnefs of that part. New plates arc fuc- 

 cfclTively added on the concave furface towards the front, 

 fo that the organ becomes fucceffively thicker and thicker : 

 they may be eafily removed in feparate (Irata, and are fliorter 

 and (horter as they are placed more and more towards the 

 front. 



Vol. XIX. 



Thefe lamina, compofing the nails, feem to bo in their 

 nature nearly identical with the epidermis. Tlie moft fuper- 

 ficlal is manifeftly continuous with that organ by its edges. 

 The nails may be detached and are regenerated exaftly as 

 the cuticle is. Their vitality is as obfcurc as that of the 

 cuticle : they exhibit no trace of animal fenfibility, ncr of 

 any organic property. "Wlu^n burnt they caufe a difagree- 

 abie odour like that of the epidermis, and exhibit altogether 

 the fame phenomena. Mr. Hatchett conceives that they 

 confift, like the cuticle, of coagulated albumen. They con- 

 tain a little phofphate of lime. Maceration and codion do 

 not, however, produce in thefe organs the fame want of 

 confiftence or kind of "brittlenefs v.-hich they do i;i the epi- 

 dermis, on account of their greater folidity. The aftion 

 of acids prefents nearly the fame phenomena. Thus, on 

 the whole, the compofition, organization, and properties of 

 the nails and epidermis feem to be perfeclly analogous : 

 they make up together a perfedt infeufible covering to the 

 cutis, a ilruflure void of vital properties, and therefore 

 exercifing no vital funftions. The only differences between 

 them feem to be modifications of form and arrangement 

 arifing from the ufes of the parts which they cover. Phy- 

 fiolcgitls affign to the nails the office of fupporting the foft 

 ends of the fingers by which the fcnfe of touch is exercifed, 

 affording to the papillx a poir.t of refiftauce, and protecting 

 them from external violence. They are a fo fuppofed to 

 enable us to grafp objedls more firmly, and to take up mi. 

 nute bodies more conveniently. 



Dcuelopement of the iVa/'/j. — While the ficin is ftill pulpy in 

 the foetus, the nails poflefs confiderable I'n mnefs, but are very 

 thin. Their length at the time of birth is not proportionate 

 to what they acquire afterwards ; they do not exceed, and 

 frequently do not reach the ends of the fingers. At this 

 time their tranfparency enables us to obfcrve the livid co- 

 lour of the venous blood circulating bef tc refpiraiion, and 

 to obferve how it is fucceeded by the redder arterial fluid. 

 After birth they increafe as tlte epidermis does ; and they 

 become extremely thick in old perfons. 



Of tl^e Hah; (S^Jlhne PUcitx of £ic/jal. J— The. human 

 frau-c poffeffes much lefs of this covering than that of ani- 

 mals : the contatt of external bodies with the ftcin being 

 ia great meafure intercepted in the latter, the animal fenfi- 

 bility of the cutaneous organ muft have much fewer ex- 

 ternal relations in them, and confequently perform a much 

 lefs important part. In animals the reprodudtive and di- 

 geltive funftions feem to be the principal fources of plea- 

 fure. 



I. Hairs of the Head. — The fyftem predominates in this 

 part, covering the cranium nearly ai the bodies of animals 

 are covered. For this reafon, as well as on account of its 

 convex form, which allows it to come in contaft with bo- 

 dies by a fmall furface only, it is very little capable of afling 

 as an organ of touch. The face is lefs generally covered, 

 excepting one part in the male fex. This portion of the 

 body, in which moft of our means of communication, with 

 external objefts, as the organs of fight, Imell, and tafte are 

 alfemblecl, is not favourable in its form to the exercife.of 

 touch. The elongated fnout of moft quadrupeds enables 

 them to touch external objects, to turn and move them in 

 various dire£l!>..j, as well as to feize ihcm for food : in man 

 the former fundtions are exercifed by the hands. 



The boundary of the hair towards the front is very va- 

 riable in different individuals : and thefe varieties influence 

 the breadth and apparent height of the forehead ; the di- 

 rcdion of this part is dependent entirely on the bony ftruc- 

 ture. Hence the hair influences bu; lliglitly the expieffion 

 H h of 



