Meckel1812-1 Anatomy 2-10

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Meckel JF. Handbook of Pathological Anatomy (Handbuch der pathologischen Anatomie) Vol. 1. (1812) Leipzig.

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Handbook of Pathological Anatomy Volume I (1812)

Section X. Of The Cutaneous System

Article First - Of The Cutaneous System In General

A. NORMAL STATE.

§374. The cutaneous system {sysiema cwfaneitm) (1) forms a sac which constitutes a general envelop to all the other organs. It may be divided into two large sections, the external and the internal cutaneous system. The former is usually termed the skin (cutis) or the common integuments (tegumenta communia). The second is the system of the mucous membranes (membranæ mucosae). Although they differ much, they are only modifications of one and the same type, as they are uninterruptedly continous with each other and in fact are similar in form, in composition, in qualities, and in functions.

§ 375. The external form of this system is that of a sac turned on itself, andconsequently double. From this arrangement openings are formed both in the upper and in the lower half of the body, by which the external and the internal cutaneous, systems communicate and are continuous with each other.(2) These openings generally lead into the chief portion of the mucous membranes. The latter form a tube which extends the whole length of the head and the trunk, and is called the alimentary canal. This canal, which has appendages in several parts which give rise to most of the viscera, presents above the openings of the mouth and nose, and below that of the anus. This part of the internal cutaneous system extends above the diaphragm into the cavity of the nose and that of the mouth, and also to their appendages, the salivary glands, and continues by the nasal canal, with a small process in form of cul-de-sac, comprising the tunica conjunctiva and the lachrymal ducts. The mucous membranes of the nose and mouth reunite in the pharynx, forming one, which divides lower down into two branches, the anterior for the trachea and the lungs, the posterior for the alimentary canal. The internal membrane of the respiratory system is the largest cul-de-sac presented by the internal cutaneous system at its upper part. The posterior branch gives olF another to the internal ear. Below the diaphragm it furnishes new culs-de-sac, which ramify, and extend to the liver and pancreas. Forming then the most internal layer of the alimentary canal, it terminates in the anus, where it is continuous with the external cutaneous system.

(1) Willbrand, Das Hautsystem, in alien seinen Verzweigungen, Giessen, 1813.— Hébréard, Mémoire sur l'analogie qui existe entre les systèmes muqueux et dermoïde, in the Mém. de lasoc. méd. d'émulation, vol. viii. p. 153.

(2) A. Bonn, De continuationibus membranarum, 1763.

Besides this general internal cutaneous system, we find others also, both in the upper and the lower parts of the body, which only represent branches of the culs-de-sac ; these are, 1st, the internal membrane of the meatus auditorius externus ; 2d, that which covers the internal face of the eyelids, the anterior face of the eye, and the lachrymal ducts ; 3d, the mammary glands ; 4th, the mucous membranes of the genital and urinary systems, which commence by a common opening.

It is impossible to overlook the gradation which exists from the absolute insulation of some parts of the internal cutaneous system, to its perfect union in a single organ. The general system of the mucous membranes of the upper and lower parts of the body, of which we can in imagination place the origin in the mouth and intestinal canal, forms an uninterrupted cavity. That of the eye communicates with it only by a narrow channel, but is not insulated from it, unless after leaving the class of reptiles. That of the mouth and of the meatus auditorius externus are connected with each other in the membrane of the tympanum, but they do not form one cavity. Thé membrane between the orifice of the genital . organs and the anus so much resembles a mucous membrane in its softness and its abundant secretion that we are almost authorized to say it unites the two openings, and really blends them in one. Finally, the mucous membrane of the mammary glands is the only one which is wholly distinct from the general internal cutaneous system.

§ 376. The whole cutaneous system is then formed of two large canals, one narrow and provided'with appendages in form of culs-de-sac, the intestinal canal ; the other broader, the common integuments, which also possesses some processes in cul-de-sac, which proceed internally. It every where presents two surfaces, one of which is loose, the other adherent. In the common integuments, the loose surface is external, and the other internal ; the contrary is the case in the mucous membranes. Thence it follows that we may consider the two sections of the system as two canals, one of which would be folded on itself.

The internal face of the cutaneous system is attached directly or indirectly to the muscles by a short cellular tissue. With the external system this union is generally direct ; for the aponeuroses are almost always interposed between the muscles and its internal face, so that the functions of the muscles it covers are rarely in relation with its own. With the internal system, on the contrary, it is direct ; for the mucous membrane is separated from the muscular membrane only by cellular tissue, which is the same as itself in regard to structure and functions,. The external cutaneous system envelops the voluntary muscles ; the internal circumscribes most of the involuntary or hollow muscles.

The loose surface of the cutaneous system everywhere forms folds, projections, and depressions of different kinds, which increase its extent more or less permanently.

§ 377. In considering the cutaneous system as a sac folded several times on itself, we do not propose to give a history of the origin of the different parts of the skin, nor to pretend that the different excavations are hollowed from without inward, in the midst of a mass which is at first solid and homogeneous, so that the upper and lower cavities of the intestinal canal meet half-way, while the others not extending so far would still preserve their appearance of cul-de-sac. There are some facts which seem to favor this hypothesis. Thus the openings do not at first exist, until about the sixteenth w-eek of uterine existence, and the upper and lower portions of the intestinal canal which are separated from each other not unfrequently form a cul-de-sac, each on its side, But these phenomena do not prove that the internal portions of the cutaneous system arise from the prolongation of the external inward. We can also explain satisfactorily the non-existence of openings in the commencement without having recourse to this hypothesis, and by admitting that the skin gradually tears in the place where they exist by the progress of the formation of the cavities proceeding from within outward. This manner of viewing the subject appears more accurate than the other, since in regard to the second argument favorable to the latter ; 1st. The place where the separation exists between the upper and the lower extremities of the intestinal canal is not always the same ; being often situated in a very distant part ; it is usually connected with one extremity only, mo.st frequently the lower, and consequently in this case it would follow that the internal portion of the skin is not developed except from a single opening. 2d. The upper and the lower extremities not unfrequently do not exist, and we find several perforations along the passage of the internal portion of the skin. 3d. The same arrangement is observed in other processes of the skin, terminating also in cul-de-sac, as in the urinary apparatus and the genital system, where, if we except the closed extremity, the extent of which is frequently considerable, it not unfrequently happens that the internal and tire external parts are perfectly developed, while, according to the above mentioned hypothesis, their formation should have been arrested where the intermediate partition exists. It is more correct then to admit that the internal part of the skin is formed from within outward ; that it probably takes its departure from several different points ; that these join as they are developed and then unite to the common integuments, making wnth them an entire whole.

§ 378. The cutaneous system is essentially composed of several layers which may be considered as so many separate systems or only as the different parts of the same system. It seems more convenient to follow this latter method, because by it we arrive at a better knowledge of the whole system. These different layers are, 1st, the derma (derma, corium) ; 2d, the papillary tissue (textus papillaris) ; 3d, the rete mucosum [rete Malpighii) ; and 4th, the epidermis (cvticula.)

Bichat has separated the epidermis from the skin, and has considered as separate systems several parts described by us (§ 16) as appendages to the epidermoid system ; but they are so intimately connected with each other, so identified in different parts, that it does not seem proper to insulate them. We may then consider all these layers generally in the whole cutaneous system, and then particularly in each of its two sections.

§ 379. The derma is the strongest, the firmest part, and the base of the whole cutaneous system. Always united to the adjacent systems, it adheres to the muscles, in the external skin by its internal face, and in the internal skin by its external face. It is white, soft, of variable thickness, having but few vessels and nerves, elastic, capable of contracting and extending to a considerable extent ; it does not possess a high degree of vitality and when destroyed is not reproduced. Its consistence and thickness in different parts of the body vary very much : generally speaking they are greater in the external than in the internal cutaneous system.

§ 380. The papillary tissue {textus papillaris) which is applied to the loose surface of the dermis is in reality only a greater development of it, being composed of mucous tissue, of vessels, and of nerves ; it has the form of small, regularly arranged tubercles which vary extremely in the different parts of the cutaneous system in volume and form. These tubercles increase the extent of the system still more than the folds (§ 377) which support them. The extreme sensibility of the cutaneous tissue depends upon them.

§ 381. The rete mucosmn {rete Æalpighii) is a mucous and semifluid substance having an immense number of capillary blood-vessels. It is more readily distinguished from the papillary tissue and the epidermis in the external than in the internal cutaneous tissue. In this tissue and in the preceding the processes of nutrition take place most actively.

§ 382. The epidermis {epidermis, cuticula) is whitish, solid, brittle, without vessels or nerves, and entirely insensible. It receives a perfect impression of all the irregularities of the layers which it covers. We cannot always insulate these latter in the internal cutaneous system. It becomes much thicker by friction, and is reproduced entirely after being destroyed.

§ 383. We also find in several parts of the cutaneous system simple glands, a species of round bursæ, which vary in size and are called in the internal cutaneous system, the mucous glands or crypts {glandulæ s. crypto?, mucosæ), and in the skin are termed the sebaceous glands {glandtdœ sebaceœ).

§ 384. In those parts where the external and the internal cutaneous systems are continuous with each other, the former becomes thinner, smoother, finer, and sometimes redder than usual, as in the lips. The general characters marking the commencement of the latter are, that the epidermis is more easily detached from the subjacent layers than in the rest of its extent.

§ 385. The cutaneous system envelops all the other organs and forms an entire whole ; but at the same time it connects the organism directly with external objects, for it continually absorbs materials from without and expels them within ; it establishes a limit, a sort of bridge between the individual organism and the rest of nature. It is in fact the most important part of all the organs of the nutritive hfe. Hence the frequerit diseases in this system and its great influence on the general health, and the part it takes in all the changes which supervene in the organisation ; hence, also, the close sympathy between all its parts, both in the healthy and the diseased states.

§ 386. The cutaneous system diflfers in the sexes : it is much thicker, firmer, harder, and less sensible in the male than in the female. It varies at different periods of life, as follows ;

1st. It is less extensive in the early periods of existence, not only from the deficiency of some parts, as the extremities, but the intestinal canal is shorter and narrower, and the folds appear late.

2d. It varies in form. At first both the intestinal tube and the anterior part of the body is open ; there are not two canals opening into each other, but only two semi-canals.

3d. There are at first more vessels and nerves, whence the process of nutrition is then carried on more actively.

4th. It is much thinner in the early periods of life ;

5th. It is then more loosely united to the subjacent parts ; and,

6th. There is more analogy between the internal and the external portion.

B. OF THE CUTANEOUS SYSTEM IN THE ABNORMAL STATE.

§ 387. The cutaneous system reproduces itself after having been destroyed, but not perfectly : hence we can always distinguish cicatrices from the true skin. We shall enter into more details upon thk subject when treating particularly of the external and the internal cutaneous systems.

§ 388. The congenital deviations of formation in this system are either its total deficiency or that of some of its layers, and its superabundance, as seen in the formation of abnormal appendages. The accidental anomalies of formation, if we except mechanical injuries, almost always result from alterations in texture, to which the cutaneous system is very subject, because of the circumstances mentioned above (§ 385). Beside those diseases in which it participates with other parts, it is often the seat of acute or chronic inflammation. Accidental tissues are frequently developed either in its proper substance or in the subjacent mucous tissue. Other alterations in its texture, for instance ossification, are rare.

Article Second - Special Remarks On The External Cutaneous System

A. OF THE EXTERNAL CUTANEOUS SYSTEM IN THE NORMAL STATE.

I. OP THE EXTERNAL CUTANEOUS SYSTEM IN GENERAL.

§ 3S9. The external cutaneous system(l) or the pïoper skin (cutis) envelops the external surface of the wholebody and forms a close sac which possesses its exact form, and is continuous Avith the internal cutaneous system in those parts previously mentioned (§ 375). The skin differs from the internal cutaneous system generally, in being thicker, firmer, dryer, and less vascular. As we have already remarked generally on its form and composition, we have only to describe its component layers.

§ 390. The derma (corium. derma) is a white, solid, and dense tissue, which differs in several respects.

Generally considered, it is composed in great part of layers which are very distinctly seen on its internal face and after maceration. These layers are produced by a substance very analogous to fibrous tissue;(2) their direction is oblique from within outward: they are also narrower on their external than on their internal face, and the vessels, the nerves, and the hairs pass through the former. This laminar tissue is continuous in many places, for instance, in the nucha, the back, the abdomen, the sole of the foot, the articulation of the hand, and in that of the foot, with the subjacent fibrous tissue which it resembles almost entirely, in the palm of the hand and in the sole of the foot, by its shining and evidently fibrous texture. But in most of the cutaneous tissue, especially the trunk, and in all parts of the limbs, its fibrous structure is less apparent and its connections with the subjacent tissue less intimate. We find no trace of fibres in the derma of the back of the hand, of the sole of the foot, of the forehead, of the scrotum, of the labia pudenda, and of the penis, "when the substance is perfectly homogeneous.

(1) In addition to the works which have been quoted, we refer to Malpig-hi, De externo tactus organo, in Epist., London, 1686, p. 21-23. — Hoffmann, De cuticulâ et cute, Leipsic, 1687. — Limmer, De cute simulque insensibili transpiratione, Z,erhst, 1691. — A. Kaaw, Perp. Hipp.sic dicta, Leyden, 1738. — F. D. Riet, De organo tactus, Leyden, 1743. — J. Fantoni, Dc curp. integumentis, in Dies, anat.' VII. renov., Turin, 1745, n. i. — Lecat, 'Traite des sens, Amsterdam, 1744. — Cruikshank, Experiments on the insensible perspiration of the human body showing its ajfnity to respiration, London, 1795. — C. F. Wolff, De cute, in N. C. Petrop., vol. viii. — G. A. Gaultier, Recherches sur Porganis. de la peau de l'homme, et sur les causes de sa coloration, Paris, 1809. — Id., Rech, sur l'org.cutané,'t?a.r\s, 1811. — J. F. Schroeter, Das menschliche Gefühl oder organ des Getostes nach den Abbildungen mehrerer herümhten Anatomen dargeslcllt, Leipsic, 1814. — Dutrochet, Observations sur la structure et la régénération des plumes, avec des considérations sur la composition de la peau des animaux vertébrés, in Journal de physique, May, 1819. — Id., Observations sur la structure dc la peau, in Journal complémentaire, vol. v.

(2) Osiander, from observations on the skin of the abdomen of women who died in child-bed, asserts that the fibre which forms the dermis is distinctly muscular on the internal face of the skin. F. T.

The dermis varies much in thickness. It is undoubtedly thickest on .the back of the hand and in the sole of the foot, and thinnest on the eye-lids, in the mammae of the female, in the scrotum, the labia pudenda, and the penis. It is thinner in the upper than m the lower extremities, and is thicker and firmer on the skull than on the face.

The dermis under the nails presents a peculiar arrangement, which we shall mention when speaking of these last, because all the layers of the skin are jointly modified in them.

§ 391. The skin is often wrinkled or folded, which depends on the different states of extension or contraction of the, sl^i and subjacent parts, or on other causes.

The folds of the first kind are produced by the action of the muscles or by the diminution of fat below the skin in aged persons, and because of its slight degree of elasticity. In fact they result from the circumstance that certain muscles directly beneath the skin, or at least their tendons, act frequently wliile the sldn is not sufhciently elastic to contract and to dilate m the same proportion, or because this membrane becoming still less elastic in advanced age does not contract, while the fat which distended it is absorbed, and it is therefore folded or wrinkled.

Other folds depend on the papillary tissue of the skin. They are very regular, small, compact, and curved. They are very manifest in the palm of the hand and in the sole of the foot. Each of these folds is composed ultimately of two others, for normally their upper face is sHghtly depressed, and the adjacent folds are separated from each other by deeper furrows.

§ 392. Below the dermis, in the panniculus adiposus which it covers, wind a great many subcutaneous vessels {vasa subcutanea) : of these the veins are very considerable, and are always broader than the deepseated veins. From these cutaneous vessels arise those which are expanded in the substance and on the surface of the dermis, most of which only pass through it to be expanded in the latter, so that the tissue of the skin is not very vascular. The same is true of the nerves.

§ 393. In some places, for instance at the commencement of the meatus auditorius externus, at the end of the nose, at the edges of the eyelids, around the anus, the vulva, and the nipple, are considerable openings from whence comes an oleaginous fluid which hardens quickly. These openings lead into small culs-de-sac called the sebaceous glands {glandidÅ“ sebaceæ). As the whole skin exhales an analogous substance, we might be led to think that these glands exist every where ; but it is impossible to demonstrate tliis. Probably the bulbs of the hairs should be considered as organs corresponding to them in structure and in functions (§ 410), or rather we must regard these glands as enlarged bulbs of the hairs which are more developed, since no hairs come from them, and they are found exactly on the common borders of the external and of the internal, cutaneous system. It would seem also to result from this, that the development of mucous crypts in the internal cutaneous system corresponds to that of the hairs and the epidermis in the external cutaneous system.

§ 394. The papular u lissm {lexlus papillaris) {1) of the skin is composed of small processes situated on the external surface of the dermis, particularly on the elevations of the second kind which this latter presents ; these processes are called papilkc of touch {papillÅ“ iactiis). Each elevation presents two ranges of these papillæ, which however are so connected with each other that they may be considered as forming but one. Like the eminences on the surfaces of which they are seen, they are vei^ manifest in the palms of the hands, in the soles of the feet, in the in the glans penis,(2) and in the mammæ.(3) Their surface is villous. In all other parts they are less distinct, even when the epidermis is removed. Even in the preceding regions we finä none between the elevations in which the papillæ of touch are situated.

The latter are composed of nerves and of fine branches of the cutaneous vessels. According to Gaultier, they principally give the color to the sldn. But this anatomist seems to have confounded them with the vascular tissue which covers them.

§ 395. The external face of the dermis and of the papillary tissue is covered with a fine vascular network, composed ofnumerous central points united' by many anastomosing vessels which are very apparent and regularly arranged.

§ 396. Proceeding from within outward, we find next to the dermis the rete mucosum, or the rete UWalpighii, a mucous homogeneous substance which may be divided into two or three separate layers. (4) It has no openings v/hich allow the papillæ of touch to communicate with the epidermis, but only depressions which correspond to them, and within which they are imbedded as in so many sheaths. This layer is the principal seat of the color of the skin, since in the negro the dermis is as white as in the European, (5) while the rete mucosum always presents the peculiar color of each race. Usually it is considered single, but we have reason to think it compound. Gaultier assigns to it three layers, the first two of which he calls the internal and the external tunica albuginea {tunica albuginea interna et externa)^ because of their color, while he calls the third the hroim substance^ in the negro, where it is very apparent. Of these three layers thé inter (1) Hintze, De papillis cutis tactui inservientihuSy'Leyde.rt, 1747.

(2) B. S. Albinus, De integumentis glandis penis ; loc. cit., lib. iii. c. ix.

(3) B. S. Albinus, Depapillis mammÅ“ et papülæ muliebris ; loc. cit., c. xii.

(4) B. S. Albinus, Quœdam de modis quibus culicula cum corpore reticulari de cuti abscedit, in Annot.-acad., Leyden, 1754, 1. i., c. i. De cognatione et distinctione cuticulæ et reliculi, ibid. c. ii.—De reliculi foveolis vaginisque quibus papillæ continentur, ibid. c. iii. — Nonnulla de usu ct ralione reticuU et cuticulæ, ibid. c. v.

(5) B. S. Albinus, De sede ct causa coloris Æthiopum et ceierorum hominum,Lcyden, ,1737.

nal is the thickest and the external is thinnest : both are white ; the middle is colored, but less so than the vascular tissue, so that it cannot be regarded as the principal seat of color except in the negro. Cruikshank has found between the dermis and the epidermis of a negro, who died from small pox, fom* layers besides the papillary tissue ; the internal very thin, a second in which the variolous pustules were developed, a third which was thicker, the proper seat of color, finally a fourth which was whitish, and which he considered the external layer of the third. • This description agrees pretty well with the preceding.

The layers, situated between the papillary tissue and the epidermis, which form this membrane, usually remain united to the epidermis when the latter is separated by putrefaction or boihng ; but they sometimes adhere to the dermis.

§ 397. The epidermis, or cidicle {epidermis, cuticida),{l) is a membranous, homogeneous, thin, semi-transparent expansion, whitish in the European, light gray in the negro, forming the most external layer of the skin, covering the internal layers in every part, and adhering to them intimately. It- thus presents the same folds and thé same inequahties as the latter, and we see on its internal face round depressions which correspond to the papillæ of touch. Its external face is smooth, while the internal is very uneven ; it is finnly united to the subjacent layers ; but ha certain cases this union is entirely destroyed either during life or after death : it seems to take place by numerous small filaments(2) which are perceived very distinctly in the palms of the hands and in the soles of the feet, if the skin be immersed into boiling water, and the epidermis be detached from the dermis. It is however dithcult to determine the nature of these filaments. Bichat considers them as the extremities of the absorbent and exhalent vessels;(3) but we have never been able to fill them, even when the cutaneous vessels had been perfectly injected ; and Hunter has succeeded no better than ourselves. Might they not have been produced from the mucous tissue by the process of boihng ? And if this be false, are they really hollow ?

The same uncertainty exists whether the epidermis be filled with holes called pores, or whether it be only thinner in those places where these pores seem to exist. Many observers, as Leuwenhoeck(4) and Bichat, particularly the former, admit that the epidermis is porous, and Bichat asserts that the oblique direction of these pores alone prevents them from being seen. Others, on the contrary, as Meckel(l) and Humboldt,(2) deny the existence of these pores. We have never been satisfied of the presence of these openings, and their existence is not necessary, since the exhaled fluids can escape very well through the thinner parts of the epidermis.

(1) C.G. Ludwig-, Decuticulâ, Leipsic, 1735. — Fabricus ab Aquapendente, De totius animalis integumentis, ac primo de cuticulâ et iis quœ supra cuticulâ sunt, in 0pp. omn., Leipsic, 1687, p. 438-452. — J. F. Meckel, De la nature de l'épiderme et du réseau qu'on appelle malpighien , in Mêm de Berlin, 1753, p. 79-97 — Id., Nouv. obs. sur l'épiderme et le cerveau des negres, ibid. 1757, p. 61-71. — B. S. Albinus, De incisuris cuticulæ et cutis; loc. cit., c. iv. — A. Monio, De cuticulâ humanâ, in IlbrA-s, Edinburgh, 1781, p. 54. — J. T. Klinkosch, De verâ naturâ cuticulæ et ejus régénératione, Prague, 1771. — Herman!, De verâ naturâ cuticulæ ejusque regeneratione, Prague, 1775. — Mqjon, Sull' epidermide, Genoa, 1815.

(2) Hunter, Med. obs. and inq., vol. ii. p. 52, 53, tab. 1, fig. 1, 2.

(3) Gen. Anat. vol. iii. p. 351.

(4) Arcan. nat. ep. phys., 43.

The thickness of the epidermis is nearly uniform, except in the palms of the hands, and particularly in the soles of the feet, where it is thicker. In fact, friction increases its thickness, and renders it callous in those two parts ;(3) but that this difference has not entirely a mechanical origin, is proved by the greater thickness of the epidermis of the palm of the hand and sole of the foot even in the fetus(4). This is the reason that it is more difficult to detach it from the subjacent layers in these two parts of the body.

The epidermis is usually formed of one layer only ; but we observe several which are very distinct in those parts where it is thickest. We have observed this several times in the palm of the hand and in the sole of the foot.

§ 398. The epidermis is essentially only the rete mucosum coagulated and hardened. It belongs then properly to the mucous tissue. It is entirely destitute of nerves and vessels, and is consequently dry and insensible. It is completely regenerated by the drying of the rete mucosum. The appearance of the vascular structure presented by it depends either on some extravasation or on the adhesion of a portion of vascular tissue. It has no power of contraction, and but a slight degree of extensibility

The epidermis moderates in part the impressions made on the papillæ of touch in the skin, and in part opposes evaporation. Hence a blister not unfi'equently causes all the serum of the mucous tissue in dropsy to escape in a short time. Hence too the skin not only dries ra.pidly in those parts where the epidermis has been removed either before or after death, but it also adheres intimately to the subjacent organs, while that of the adjacent parts which has preserved its epidermis always remains moist.

That the epidermis arises from the hardening of the rete mucosum is proved by the fact that it is partly the seat of color in the skin, for it always presents the same tint as the rete mucosum, but it is less distinct.

§ 399. The epidermis appears early ; it is already seen distinctly in the fetus of two months ; it is then even proportionally thicker. Besides, the considerable growth of hairs and the formation of the caseous substance {vernix caseosa) with which the skin of the fetus is covered, prove the great activity of the epidermoid system at this period.

We may state, as sexual differences, that it is softer and thinner in the female than in the male.

(1) Mérti. de Berlin, 1763, p. 63.

(2) Uebcr die gereizte Muskel- und Nervenfaser, vol. i. p. 156.

(3) Nürnberger, De cuticulae frictione cowprimentc callosä, Wittenberg, 1789.

(4) B. S. Albinus, De sede col. cutis, p. 9. _ •

The races of the human species also present some differences. Although several anatomists, among others Malpighi(l) and Littre,(2) affirm it is white in the negro, we now know that it has a grayish, brownish tint. We agree with the opinion of Santorini,(3) Ruysch,(4) Albinus, (5)Meckel,(6) and SÅ“mmening.(7)

It is a little coarser in the negro than in the European.

II. OF THE MODIFICATIONS OF THE EXTERNAL CUTANEOUS SYSTEM, OR OP THE APPENDAGES OP THE SKIN, THE HAIR, AND THE NAILS.

§ 400. The hairs and the nails are generally considered only as appendages of the epidermis. But in our opinion this is incorrect ; for the nails and the hairs are in fact modifications of the whole cutaneous system, although the epidermoid system and that of the rete mucosum predominate in the most of then length. In fact the dermis below the nails is peculiarly modified, and corresponding variations are observed in the other layers of the skin. We must then consider as belonging to the nail not only the epidermis which is particularly modified, but also the whole cutaneous texture. The same is the case with the hah, for their bulbs are evidently, analogous to the dermis.

1st. Of the nails.

§401. The epidermoid portions of the nails, or the proper nails (ungues), (8) are broad, hard, shghtly convex, and oblong layers formed at the ends of the backs of all the fingers and toes, and which cover the anterior part of the thhd phalanx, projecting forward and on the two sides.

We distinguish in the nails three portions, the posterior or the root, the central or the body, and the anterior or the free extremity.

The root (radix unguis) is concealed under the skin, and is softer and thinner than the other two parts. It gradually becomes thinner, and terminates in a rounded edge. It is one fifth or one sixth of the whole length of the nail. The central part, the body, is much larger than the other two parts, and its internal face adheres intimately to the skill, while the external face is unattached. Its posterior part varies proportionally in extent according to the subjects, and almost always diminishes from the thumb to the fifth finger : it is white, convex forward, and concave backward, and is termed the crescent (lunida).

(1) Exerc. dc externo tactus organo.

(2) Hist, de I'ac. des sc. de Paris, 1702, no. 13, p. 40.

(3) Observ. anat. Venet. 1724, 1. i. p. 1.

(4) Curæ renovatæ, no. 59, 87.

(6) hoc. cit., p. 6.

(6) Mêm. de Berlin, 1753, p. 93.

(7) lieber die körperlichen Verschied, des Negers vom Europrœ, lT85, p. 45.

(8) Frankenau, Z)e unguibus, Jena., 1696.— Ludwig“, De ortu et structura unguium, Leipsic, 1748. — B. S. Albinus, Deungue humano ejusque reticulo, itemgue de cutis loco, qui unßue tactus ac de loci istius papillis, in Annot. acad. vol. ii.-xiv. — De natura unguis, ibid. c. xv. — Bose, De unguibus humanis, Leipsic, 1773.— Haase, De nutritions unguium, Leipsic, 1774.— Nürnberger, Meletemata super digitorum unguibus, Wittenberg, 1786.

The anterior is much greater, and appears reddish. The/ree exlremiiy projects beyond the skin, so that its two faces are entirely free. It is tire thickest part of the nail, which consequently diminishes gradually in thickness from behind forward. The length of this extremity is not fixed, and depends on the greater or less degree of attention with which it is cut. Left to itself,- it becomes very long, thick, and pointed.

§ 402. The nails are connected only with the epidermis, and adhere to it so intimately in all their circumference that they are retained firmly in place. The nail ig sbghtly covered behind and on the sides by the epidermis which is reflected forward from below. Behind, this membrane projects on the concave and thin edge of the skin wdiich covers the posterior part of the nail, forms a small groove often separated from the skin by a kind of channel, and which is intimately connected before with the anterior edge of the crescent. Thence the epidermis goes backward, insinuates itself below the portion of the skin which slightly projects above the nail,is reflected on the inferior face of the nail, and is continuous with it forward. On the sides, the epidermis projects as it does behind, but it is not extended foward, and is also continuous with the edge of the nail. The epidermis having covered the anterior extremity of the finger 1-eaves the skin, and attaches itself to the anterior convex edge of its central and adherent part, and blends itself with its substance.

Thus, the nail (in the common sense of the word) is only a thickened portion of the epidermis, which detaches itself, like this latter, from the subjacent layers of the skin.

§ 403. But these subjacent layers present of themselves some modifications. The dermis is thicker, softer, has no layers, and is not attached to the nail by any prolongation. Under the body of the nail, it is very red and more vascular than in the other parts. Under the root and the crescent, on the contrary, (if we except the nails of the toes, which usually have no crescent,) it is white, so that the whiteness of this semilunar spot does not depend on the nail, but on the skin. Its upper face has very distinct longitudinal fibres, especially in its reddish anterior portion, which is the most extensive. These fibres may be compared to the papillœ of touch, and the internal and inferior face of the nail, which is soft and also provided with very distinct longitudinal fibres, may be compared to the rete mucosum intimately connected with them. In the small nails of the toes, which are imperfectly developed because they are compressed, we discover neither the fibrous structure of the skin nor the rete mucosum, but the projections and excavations which correspond to them are irregular and more similar to papillœ.

§ 404. The epidermoid portion of the nail is composed of superimposed layers, the external of which extends the whole length, while the internal gradually diminish from behind forward, so that the most anterior are the shortest ; these, too, are also the softest, and become, at least apparently, more fibrous. The structure of the nails is homogeneous, like that of the epidermis ; they have neither vessels nor nerves.

§ 405. The epidermoid portion of the nails presents no trace of sensibility or contractility. The vital phenomena which take place in them are very slow, except the acts of growth, which proceed rapidly, as is proved % their continual increase. § 406. The nails begin to appear in the fifth month of fetal existence, and are very imperfect at the ninth.

2d. Of the Hairs.

§ 407. The hairs {pili, crines){l) are filaments of various lengths, always thin in proportion to their length, about g-i-g- of an inch in diameter, more or less cylindrical and usually smooth. We rarely 'perceive at intervals these swellings, which are apparently produced by some disease. Their attached extremity, called the bulb {bulbiis,) is a little thicker and always soft, the other is slightly pointed. In the normal state, they are seen only on the external cutaneous system, or the skin properly so called, covering all its parts, except the palms of the hands and the soles of the feet, where it is very remarkable that that the epidermis is considerably thick. We must remark in general,

1st. That principally around these points where the external cutaneous is continuous with the internal cutaneous system, we find numerous hairs, which assume a peculiar arrangement, as on the edges of the eyelids, in the nostrils, at the entrance of the ears, around the mouth, the anus, the vulva, and the mammæ.

2d. That the law of polarity exists between the parts on which they grow in abundance ; as in the head and the pubis, on the chin and the anus, on the back and the belly.

§ 408. The hairs are composed of two substances, an external and an internal.

The external., which surrounds the other like a sheath, has all the properties of the epidermis. It is always transparent, white, and very difficult to destroy ; it is continually reproduced, and in the bulb or follicle is more or less evidently composed of several layers.

Under this sheath we find a colored substance formed of about ten filaments, probably vessels. The form of this substance resembles that of the hairs, but it is much thinner than the internal envelop. It is imbedded into the centre of a fluid, which being partially lodged in the canal formed by the filaments jxirtly scattered between theîn and the external envelop, unites them together, and constitutes, with them, the marrow of the hairs.

(1) P. Chirac, Lettre écrite à M. Regis sur la structure des cheveux, Montpellier, 1668. — Malpighi, De pilis observationes ; in Opp. posth., London, 1697, p. 93-96. — M. J. J. Bajerus, De capillis diss., Jena, 1700. — O. Zaunslifer, Diss. exhibens historiampilorum in homine, Leyden, 1738. — Meibomius, Depiiis eorumque morbis, Helmetadt, 1740. — G. A. Langguth, De pilo parte corp. hum. non ignobüi, Wittenberg, 1749. — P. Grutzmacher, De humore cutem inungente, Leipsic, 1748.— e. P. L. Withof, Anatome pili humani, Duisburg, 1750, in 4to. — J. H. Kniphof, De pilorum usu, Erford, 1754. — J. P. Pfaff, De varietatibus pilorum naturalibus et prÅ“ter naturalibus, Halle, 1799. — Rudolphi, De pilorum structura, Gripswald, 1806. — Grellier, Dissertation sur les cheveux, Paris, 1806. — Rudolphi. Auf satz über Hornbildung ; in Aèhandlungen der Wissenschaften von Berlin, 1818, p. 180. — Rowland, An historical, philosophical, and practical essay on the human hair, London, 1818' — Buek, Diss. de pilis eorumque morbis, Halle, 1819.— Aegidi, Dissertatio de pilorum anatomiâ, Berlin, 1819. — Hensinger, Remarques sur la formation des poils, in Journal complémentaire du Diet, des sc. mêd., vol. xiv., p. 229. — Id., Sur la régénération des poils, same journal, vol. xiv., p. 339.

This internal substance corresponds undoubtedl.y to the rete mucosum of the skin, and is the coloring matter of the hairs, which whiten when it disappears.

§ 409. The hairs do not seem to receive blood-vessels, at most we can perceive but a few, and these very seldom, in the inferior swelled portion of the bulbs, which is provided with one or more openings. Through these come the blood-vessels, and probably the fine nervous filaments. In fact we cannot plainly distinguish the nerves, but the analogy derived from the coarse hairs of animals and the pain occasioned by their removal, authorize us to suspect their existence. It is, however, certain that the nerves do not extend beyond the bulb.(l)

§ 410. The hairs are situated under the skin in the mucous tissue, which is almost always filled with fat. The largest are found there, (although this arrangement is not so apparent in regard to the smaller ones,)in the small, closed, thin, whitish and very vascular envelopswhich loosely surround them, pass through the openings in the dermis (§ 390), thus arrive at the epidermis, continue with it, remain fixed to its internal surface as small hollow prolongations, when it is detached from the dermis. There is no adhesion between the hairs and the envelops except at the extremity of the bulb, so that in this place the hairs appear more or less villous on their surface. A thin fluid exists betvmen them and the surrounding sac, which in the dense hairs of animals is real blood.

§411. From the want of nerves, the hairs are insensible. They have no contractile power ; but the formative power is much developed. They grow constantly, and lengthen even after death, or when detached from the body. (2) Thus they are reproduced after having been lost from accident, but not when vitality is absolutely extinct. They possess great strength, and are with difficulty destroyed, undoubtedly because of their external envelop.

§ 412. According to the latest researches of Vauquelin,(3) the hairs are cemposed,

1st. Of an animal substance which constitutes their base, and is very similar to dried mucus, and certainly comes from the external envelop.

2d and 3d. Of two oils, one white and concrete, the other blackish, on which their color depends, at least in part, and which undoubtedly belong to their internal substance, since they vary according to the color of the hairs, and are not colored in those which are white.

4th. Of iron.

5th. Of a little of the oxide of manganese.

(1) Rudolplii has followed the nerves into the bulbs of the mustaches of the seal — ag has also Andral, jun. See his note : Sur les nerfs qui se rendent aux mustaches du phoque ; in the Journal de physiologie expérimentale, vol. i., 1821, p. 73. F. T.

(2) Krafft, in Nov. corn. Petrop., vol. ii., p. 24.

(3) Annales de chimie, 180Ö, vol. Iviii.

6th. Of the phosphate 7th. Of the carbonate

I of lime.

8th. Of silex.

9th. Of a considerable quantity of sulphuf § 413. The hairs differ from each other very much in the different regions of the body. The hairs of the head {coma s. capilli s. cœsaries) are the longest, the strongest, the most numerous, and the closest

Next come those of the beard, the hairs of which are distinguished from those of the head in being more distant from each other.

Next come those of the pubis, of the axilla, of the anterior face of the thorax, and of the abdomen, the eyebrows, the eyelashes, the hairs found in the nose, the anus, and those on the limbs, which become shorter and thinner as we descend to the lower part of the limb, and finally, those of the cheeks and the forehead.

The hardest and coarsest are those in the nose, and those on the face are, if we except the beard, the softest. The hairs of the pubis are the thickest ; next come those of the axilla, then the hairs of the head, next the eyebrows and the eyelashes.

The color of the hairs is usually the same in all parts of the body, but to this rule there are many exceptions. It sometimes happens, but it is rate, that a part of the hairs of the head are unUke the rest in color, more often, even usually, only some hairs are discolored, while the rest preserve their primitive color.

All the hairs of the same subject do not appear at the same time. The hairs of the head exist at birth, while the beard and the hairs on the pubis and the axilla do not appear till puberty.

§ 414. The hairs are subject to very considerable periodical changes.

The ‘skin is entirely smooth till towards the middle of fetal existence. At this time, however, it is covered with numerous short fine hairs, a kind of down {lanugo). At first these hairs have no color, but assume one as the period of birth approaches. On certain parts of the body, for instance, on the face, they are much longer than the permanent hairs which afterwards appear in these same parts. Their length is at first almost equal m every part, but at birth however, those of the head are much longer and stronger than the rest.

These downy hairs of the fetus fall some before, but most of them after, birth. They are found in the waters of the membranes and in the meconium. Those which replace them on the body do not begin to appear till puberty, when the beard and the hairs of the pubis, of the axilla, and of the trunk are developed. The hairs of the head, on the contrary, remain the same and grow much more rapidly after birth than before.

The color of the hairs generally becomes deeper in age : this rule is, however, subject to exceptions, although they are few.

Sooner or later, usually about the age of thirty, the hair begins to whiten, by the disappearance of the internal substance. A little later when the external envelop has continued for some time to grow regularly, the attachments existmg between it and the follicle in which it is contained are destroyed, and the hair begins to fall out.

of all.

The white hairs contain a colorless oil and some phosphate of magnesia, which is not found in the colored hair.

Both of these changes take place first in the longest and thickest hairs, that is, those of the head, and particularly those found on the top of the head. The hairs of the extremities change the last.

The hairs which have fallen off are rarely replaced, and those which have lost their color seldom resume it ; some examples of this phenomenon, however, have been seen.

The part which forms first is the sac which surrounds the bulb, a complete ovum, which, either in the primitive hairs or in those afterwards develôped, is already perfectly formed before the bulb, and is pierced by the hair which lengthens outwardly, as the capsule of the tooth is by the tooth, or the membranes of the ovum by the fetus. Probably its decay causes the death of the hairs ; for in old men whose hairs have fallen, we find no traces of tlrese sacs under the skin, while, when we see them as in the natural state, after those diseases where the hair has fallen off, a new growth arises from them.

§ 415. We may mention as sexual differences, that in the female the hairs are finer ; those of the head are longer, but those in other parts of the body are shorter. They are not entirely deficient in any of those parts where they exist in the male ; and in those places where they are largely developed in the male, they are also rather longer and more numerous in the female, especially when the functions and the differences dependent upon sex are not perfectly developed.

§ 416. Besides these differences arising from age and sex, the hairs present others also. In fact they vary according to the individuals, and in this relation they present, in the different human races, peculiarities, some of which are accidental, while others are very constairt :

1st. The color of the hair differs surprisingly in different individuals of the same race and of the same family. It varies from a very bright yellowish (white) to the deepest black, between which two extremes we find every imaginable shade of auburn, red, and brown. Other colors, as green for instance, cannot be considered as primitive : they depend on external influences, such as copper.

2d. As much may be said in regard to the thickness, number, and length of the hairs. Generally we may admit that the blackest are the thickest, and that the lighter are finer. Withof found in one fourth of a square inch of skin oire hundred and forty-seven black hairs, one hundred and sixty-two chestnut, and one hundred and eighty-two light hairs. This rule, however, is subject to exceptions, and the more as the hairs are not at equal distances in all individuals.

3d. The direction of the hairs is various. Usually they are even and straight ; often, however, they are more or less curled or frizzled.

The differences met with in the same nation may be considered as the differences of races. The most important ones have already been mentioned (§ 33) ; we shall only remark that these occur in all races : thus, there are negroes who have straight, long hair.

B. Of The External Cutaneous System In The Abnormal State

417. The external cutaneous system possesses in a great degree the power of reproducmg itself. (1) AU its layers are reproduced, by whatsoever cause they may have been destroyed. But they do not reappear vdth characters perfectly sinülar to those which they have in the normal state.

The dermis is less elastic, and adheres more closely to the subjacent mucous tissue, than the natural dermis ; it is in fact blended wdth this tissue, and cannot be separated from it. Like aU other regenerated parts, it is less hard and has less spontaneous activity than the natural dermis. This explams the ease with which even old cicatrices are torn, and with which the new integuments of cutaneous ulcers are sometimes entirely destroyed.

The new dermis is at first exceedingly thin, delicate, and soft, more vascular, and of course redder, than the natural dermis ; it gradually becomes less vascular, whiter, firmer, and harder than the latter, and acquires almost all the qualities of a ligament. At the same time its aspect is smooth and shining, which depends undoubtedly on the absence of the papillae of touch and on that of the hairs, as well as on the tension of the new integument and its more intimate adhesion to the subjacent mucous tissue.

Its sensibihty is less than that of the primitive dermis, doubtless because of the absence of the nervous papillae. Perhaps also it receives fewer nerves than the latter.

These different phenomena are not however seen except when the dermis has been entirely destroyed ; for when the injury is only superficial, all marks of difference disappear with greater or less promptitude.

The new dermis is covered Yvith a rete mucosum and an epidermis ; but these latter are reproduced only gradually, as the fii'st formed layers always fall off.

The color of the rete mucosum is developed the last, and this is somethnes entirely deficient. Bichat pretends that its color is not reproduced when it has been removed, and that cicatrices are white in all people ; but this assertion is not perfectly correct, for in the negro the cicatrices of small pox are black,(2) and those which are developed after all injuries of the common integuments, are as black and sometimes blacker than the rest of the skin. (3)

(1) Moore, On the process of nature in the filling up of cavities, healing of wounds, and restoring parts which have been destroyed in the human body, London, 1782, sect. ii. p.,46.

(2) Meckel, in Mem. de Berlin, 1753, p. 81.

(3) Moore, lac. cit., p. 52. — Hunter, On the blood.

The nails and the hairs also possess the restorative power to a considerable extent.

The nails are reproduced not only in their natural places, but we have also seen them developed at the end of the second phalanx of the fingers when the third has been destroyed.

The hairs are not regenerated when the dermis has been destroyed entirely ; but they grow again more or less perfectly when they have fallen off from disease.

§ 418. The diseases of the skin extend to all the layers, or are confined to some only, which remark applies also to the anomalies of its form or to the alterations of texture.

§ 419. The prmcipal deviations of formation are,

1st. Its absence. The whole skin or some of its layers only may be deficient in one point or another. The first occurs when the cavities of the viscera are not entirely closed. But sometimes the epidermis is primitively deficient without any division or fissure of the body. The same is true of the nails and the hairs.

2d. Its excess, which is manifested, when the whole skin participates in it, by the existence of a greater or less number of rounded oblong excrescences in different parts of the body, almost always attended with a want of development in other parts.

As to the different parts of the cutaneous system, the most striking example of their excess is the extraordinary length of the hairs in places where they are usually very short. This deviation of formation is almost always attended with a greater development of fat and a darker tint of the skin.

The same deviations of formation may also be secondary or accidental.

The epidermis, the hair, and the nails, die after diseases of the skin, or in other morbid states consisting essentially m extreme weakness of the vital powers ; they are then detached from the body. The epidermis is constantly reproduced ; but this is not the case with the hairs and the nails. The albinism of the hairs also results from an imperfect nutrition, for it depends upon the slow or rapid death of their internal substance.(l)

The skin and its different parts can also acquire an increase of development. The dermis thickens, the papillæ of touch become longer. Warts arise from an unusual increase of some parts of the dermis, corns and callus from the thickening of the epidermis ; a considerable development and a horny hardening of the epidermis, forms also the essence of iclhyosis. There is much affinity between these different states and the excessive growth of the hairs of the head in plica polonica, which makes the transition from deviations of formation to alterations of texture.

(1) Weclcmeyer, HUior. pa/hol. pilorum, Gottingen, 1812.

§ 420. Alterations of texture are very frequent in the cutaneous tissue. Among the first we place a want of color in the rete mucosum, the leucethiopia, or leucosis, which is usually congenital, but which sometimes develops itself during life.(l)

Besides the inflammations, to which we give different names, according as they attack the different layers of the skin or the subjacent cellular tissue, the cutaneous system is subject to a great many affections which are pecuhar to it and known by the term exanthemata, the history of which belongs to pathology. Generally in the exanthematous diseases, the skin becomes like the mucous membranes, for its vessels receive more blood, it softens, furnishes liquid secretions, and the epidermis is almost always detached from it. As to the eruptions themselves, they are usually rounded, giving origin to a local increase of the peculiar life of the tissue which from a central point extends a greater or less distance, and assumes the characters of an inflammation which almost always results in the formation of a peculiar fluid. They may be considered as very imperfect organisms, or even as more or less successful attempts to produce ova, which they resemble in their round form, and from this circumstance, that they never become otherwise than fluid. Besides, the phenomena they present in their progress are in fact the same which are observed in entire organisms from their origin till their death. The chronic exanthemata are situated principally in the thickness of the dermis, while those which are acute in their progress appear at the external face of this membrane and in the vascular tissue.

§ 421. Abnormal formations of another species are developed, at least primitively, in the subcutaneous cellular tissue : such are fatty tumors, schirrus, cancer, and fungus hematodes, which extend sooner or later to the skin itself.

§ 422. Formations of the skin sometimes appear in abnormal places ; but this is less common in regard to the dermis than to the epidermoid portions, particularly the hairs. (2)

The most remarkable peculiarities presented by the accidental formation of the hair are,

1st. They are developed in the same circumstances as the regular hairs, that is, at the same time as the fat, and in the parts resembling the skin, either those newly formed, as the cysts, or those already existing, as the mucous membranes.

2d. They perfectly resemble the normal hairs, both in theh structure, their situation, and their changes. Like them they have roots, and almost always are implanted at first very firmly ; like them also they usually fall off after a certain lapse of time, and then appear mixed with fat. It is possible, however, that sometimes their roots are implanted in the fat 'only.

(1) G. T. L. Sachs, Historia naturalis duorum leucœthiopum auctoris ipsius et sororis ejus, Salzbach, 1812. — Mansfeldt, Réflexions sur la leucopathie considérée comme le résultat d'un retardement de développement, in the Journ. compl. des sc. méd., vol. XV. p. 250.

(1) Meckel, Mémoire sur les poils et les dents qui se développent accidentellement dans le corps, in the Journ. compl. du Diet, des sc. méd., vol. iv. pp. 122 and 217. — Bricheteau, Observation de kystes dermoïdes et pileux, suivie de quelques remarques sur ces productions organiques, in the Journ. compl. des sc. méd., vol. xv. p. 298.

3d. The places in which they occur most frequently are those where the activity of formation is the greatest, as in the ovaries. They are rarely seen in the testicles, although they have been found in these organs also.

The nails, or horny productions,(l) are developed more rarely in places differing from those which have been mentioned as their usual situations. The most general coirdilions of their formation are as follows : 1st, as far as our knowledge extends, they form only in the skin ; 2d, they develop themselves in cysts filled with fluid, which they pierce from within outward ; 3d, when destroyed, they are reproduced like the natural parts ; 4th, we generally find several at the same time in the same subject ; 5th, they are more common than in any other part in the loose portion of the skin, and especially in the integuments of the head, although they are sometimes found in places where this membrane is reflected on itself, for instance in the glans.

Article Third - Of The Internal Cutaneous System

A. OF THE INTERNAL CUTANEOUS SYSTEM IN THE NORMAL STATE.

§ 423. We have already mentioned the division of the internal cutaneous system, or the system of the mucous membranes (§ 375). From the description we have given of it, it follows that this system represents a large canal extending from the mouth to the anus, presenting in its passage several prolongations and several simple or complex culs-de-sac, which comihunicate directly with the external cutaneous system. We observe besides, in all portions of the system of the mucous membranes, enlargements and contractions, which depend on the figure of the parts which it contributes to form, and the internal face of which it always lines.

The internal is much narrower than the external cutaneous system, but it is much longer and more distributed in the body.

§ 424. The external face of the mucous membranes is attached to the neighboring organs, which are almost always muscles — seldom, as in the gums, to bones — and sometimes to cartilages and fibrous tissue, as in the trachea — by a dense and solid layer of cellular tissue, ih which are the large vascular trunks which go to these membranes. This layer of cellular tissue is called the nervous coat ; and, according to Bichat, the form of the organ depends on its inner layer of mucous membrane.

(1) Caldani, in the Mem. della societa italiana, vol. xvi. p. 126. — Meckel, Sur les comes accidentelles, et en 'particulier sur celles qui viennent a,u gland, chez l'homme, in the Journ. corn, pl. des sc. mêd., vol iv. p. 91. — Bertrand, Note sur une production cornée, in the Archives gén. de méd., vol. v. p. 534.

This assertion, however, is not well founded ; for the' form of these organs is determined principally by the muscular tunic ; this is proved particularly in those places where this latter tunic is very thick, as in the uterus, the mouth, the pharynx, the esophagus, and the rectum.

In fact Bichat brings forward an cxperihnent which he believes proves his assertion. If we deprive a portion of intestine of its peritoneal, muscular, and nervous coats, and afterwards inflate the canal, the mucous membrane porjects at the place from which these coats have been removed. If a fold of the intestine be turned, and the mucous membrane and the nervous coat be removed, and it be inflated, the muscular and the peritoneal tunics also pass from the opening. But this experiment has always afforded me different results, which settle beyond a doubt that the form of the organ does not depend on its muscular coat.

In the former case, in fact, when the intestine remains in its proper place, the protrusion occurs when the muscular coat is removed, although it becomes more considerable after the separation of the nervous tunic. If, on the çontrary, the intestine be turned, the removal of the nervous and mucous coats is not followed by the protrusion of the muscular membrane, although when the latter is raised, the peritoneal coat rises slightly.

The union between the mucous membrane and the surrounding parts is not every where equally intimate. Usually, as in the whole intestinal canal, the nasal fossæ, the bladder, and the vasa defer entia, the adhesion is feebler than in some other parts, as of the tongue, the alveolar processes, and the uterus, where it is so intimate that the respective hmits of the parts can scarcely be distinguished.

§ 425. The internal and loose face of the mucous membranes is not perfectly smooth, like that of the external cutaneous system. It presents inequalities which in some parts are more distinct even than in the latter. Sometimes these inequalities depend on the great development of the nervous papillae, as in the tongue and the small intestines ; so that they are produced by these papillae and by the epidermis, that is in fact by all the layers of the mucous membrane, but also by it alone. Sometimes they give origin to folds, valves {'plicÅ“ s. valvulÅ“), formed either by the nervous coat and the mucous coat alone, or at the same time by the muscular coat. The former is much more common than the latter. Among these folds are arranged the valves of Kerkring in the intestinal canal, the folds of the internal face of the gall-bladder, of the vesiculæ séminales, and of the neck of the uterus, the wrinkles of the stomach and of the vagina. Among the folds of the second kind may be cited the pyloric and ileo-cæcal valves. These latter are found in that part where the function of the organ to which they belong requires a barrier or a line of demarkation between its different sections. The differences of the first kind are either constant or not. Thus, the folds of the intestines are always found, while those of the stomach and of the vagina are inconstant. The first, like those dependent on the development of the nervous papillae, arise from the extent of surface presented by the development of the mucous membrane ; while, on the contrary, those of the stomach appear because the mueous membrane is less contractile than the surrounding muscular tunic. The wrinkles in the vagina are inconstant for the same reason as the folds of the stomach ; for as they are more or less completely effaced by repeated distensions of this canal, this peculiarity demonstrates that their existence and their absence depend on the same cause.

§ 426. The internal differs but slightly from the external cutaneous system in its texture; but, in this respect, it varies more than the external in different parts of the body, doubtless because of the greater variety of functions it executes, according to the nature of the organs the internal face of which it lines.

The chief differences are,

1st. The manner in which the mucous membrane is bounded externally, or in which it is continuous with the surrounding parts. We have already examined this question (§ 424).

2d. The relations of the layers to each other. The mucous membranes differ from the external cutaneous system, as we cannot, in all parts, insulate the layers which constitute them.

In fact, these layers are so intimately united in almost every part of the internal cutaneous system, that ordinary means have in vain been employed to demonstrate them. Of this we have proofs in the mucous of membranes of the urinary apparatus, of the genital organs, and of most the intestinal canal, where blisters during life, and maceration after death, will not prove the existence of an epidermis, or more especially of several superimposed layers. On the contrary, the epidermis may be insulated in the mouth and the esophagus ; it is also more or less perceptible on the surface of the glans, in the meatus auditorius, in short, as before stated (§ 384), in most of those places where the internal cutaneous system is continuous with the external. It is however softer, more brittle, and detached with greater difficulty in a certain extent, than that of the skin, although in several parts, for instance in the tongue, its thickness exceeds that of the epidermis which covers most of the external regions of the body.

It is very doubtful if the epidermis exists in those places where we cannot by any means insulate it ; and although Haller, Bichat, and other physiologists, think its existence is proved by the appearance of membranes having the form of the canals from which they are expelled ; still the form of these membranes may be well explained in several other ways. In fact,

a. It is possible that these may be new formations produced by the inflammation of the mucous membranes ; which is more probable because they appear when the organs are inflamed, and abnormal membranous expansions are not only developed very often on the surface of inflamed serous membranes, but also an expansion of this kind, the caducal membrane, is normally produced, in the uterus, either by coitus followed by impregnation or by a morbid state without coitus.

OF THE INTERNAL CUTANEOUS SYSTEM IN THE NORMAL STATE. 329

b. The expelled membrane also may be itself a mucous membrane separated from its connections by gangrene, since we see the skin and other organs detached in their whole thickness from the same cause.

The existence of the epidermis as a distinct layer is not proved by the thickening, the hardening, and the dryness which the mucous membranes experience when they have been often irritated, or exposed for a time to the action of the external air. Finally, it is not demonstrated by the facility with which the mucous membranes support these unusual relations with external objects ; for all we can conclude from this is, that the mucous membranes have on their free surfaces a tissue analogous to the epidermis.

We discover also fewer traces of a distinct rete mucosum, at least unless we consider as such a whitish fluid found between the epidermis of the tongue and its papillæ.

The dermis of the mucous membranes offers as many differences ; and as they are formed in most of their extent of only a single layer, we must refer almost exclusively to this layer the principal variations they present, and which still remain for us to examine.

3d. The thickness. It varies much. The dermis of the urinary organs, of the respiratory organs, and of the genital organs, is uspally very thin ; that of the intestinal canal and of the stomach is thicker ; that of the esophagus still thicker, but always less so than that of several parts of the mouth, as the palate and the gums. The dermis of the mucous membrane of the nose has also considerable thickness.

4th. The development of the capillary .tissue. We may justly compare, as Bichat has done, the villosities {villi) of the mucous membranes to the papillæ of touch (§ 394). Like the latter, they are composed of cellular tissue, in the substance and on the surface of which blood-vessels and lymphatics are certainly distributed, and which probably receives nerves also, although we are not certain that the latter exist every where. The vessels are demonstrated by injections : this cannot be doubted when the injected parts are examined with a microscope. The nerves are seen distinctly in some parts, as in the tongue ; but farther, for instance in the intestinal canal, microscopical observations made with the most scrupulous care demonstrate only a simple granular structure in the villosities. We have not been able to observe openings in them with certainty.

The size and development of the papillæ of the mucous membranes are not everywhere the same. In several parts, as in the tongue and the small intestine, these papillæ are more developed than elsewhere, and are visible without any preparation, for instance without raising the epidermis, as is necessary in the skin. In the lips and penis they are considerable, but in those parts the epidermis covers them. Every where else they are extremely small and even imperceptible.

We particularly remark that the degree of their development is in direct relation with the wants and functions of the organs, for their volume increases in all those parts where a great increase of surface is necessary.

6 th. The glands of the mucous membranes are much more developed than those of the common integuments. They always represent culsde-sac, and are more distinct in some parts, as around the mouth, than in others, especially in most of the extent of the mucous membranes, where they exist as simple depressions. Their special properties will be mentioned when treating of the glands. We shall only observe in this place that their number and volume are inversely as those of the villosities ; of this we may be convinced by comparing the membrane of the palate and tongue with that of the small and large intestines.

6 th. The continual moisture on the internal and free surface of the mucous membranes depends on the mucous glands, on the peculiar activity of the vessels of the mucous membranes, and on their slight exposure to the drying action of the air. The fluid secreted by these glands and called mucus, varies in .the different parts, although its essential properties are everywhere the same:(l) it is insoluble in water but absorbs much of it ; it coagulates neither by heat nor cold, and when dried becomes transparent.

7th. The color of the mucous membranes is not every where the same ; usually they are light red.

8th. These membranes are considerably softer than the external skin.

9th. They are also more vascular.

But they resemble more or less the common integuments in all these relations when placed in the same circumstances, especially in the inversion and the prolapsus of parts which they cover.

§ 427. Have the mucous membranes appendages similar to the nails and the hairs of the external cutaneous system ? We discover in them parts perfectly corresponding to these appendages, only in the abnormal state, and even then only hairs (§ 422) ; but we may consider the teeth as organs having many relations with them. Bonn(2) pointed out this resemblance, which has since been better developed by Walther(3) and by Lavagna,(4) and many facts might be adduced in its support ; but we shall consider this important question in descriptive anatomy when treating of the teeth.

(1) Fourcroy and Vauquelin, in Annales du Museum, vol. xii. p. 61, 67. — Berzelius, On the mucus of mucous membranes, in. General Views of the properties of animal fluids, in the Med. chir. trans., vol. iii. p. 245-247.

(2) De contin. membr., § xvi., in Sandifort, loc. cit., p. 276. An ergo membranula

hÅ“c folliculum constitucns, cutis oris propago est, per foramenula limbi^äxoducta ? An testula, quae déin crusta vitrea vocalur continuatio ejus enidcrmidjSIÊ, piaturæ unguium quodammodo, sed magis induratÅ“? . ' '

<3) Physiologie, vol. i. p. 174, 175.

(4) Esperienze c rifiessioni sopra la carie de' denti umani coll' aggiunta di un nuoco saggio sulla riproduzzionc do' denti negli animati rosicanti, Genoa, 1812, p. 164-198.

B. OP TUE INTERNAL CUTANEOUS SYSTEM IN THE ABNORMAL STATE.

§ 428. We are deficient in observations to enable us to decide, if the mucous membranes grow again after having been destroyed, or if, where they have appeared to be reproduced, there has been only a contraction and reunion of the sound parts. (1)

§ 429. The mucous membranes present many anomalies. Their deviations of formation, especially the primitive, coincide almost always with analogous states of the whole organ, the internal face of which they line : such are, fissures, prolongations in form of sacs, contractions, inversions, &c. In these different cases all the layers vary in the same maimer from the normal state.

In fact in other circumstances the upper layers also present simultaneous anomalies : but these are of a different nature. Thus when the mucous membranes are considerably distended by their passage as hernias through the muscular coat, and which are known, particularly in the intestinal canal and the bladder, by the term diverticulmn spurium, the fibres of the muscular tunic are separated from each other.

We however observe abnormal processes which belong only to tho mucous membranes, independently of the other layers.

§ 430. These last anomalies form the transition from deviations of formation to changes of texture, since they are sometimes simple prolongations, such as the valves in the intestinal canal, but much more frequently excrescences, new formations, the texture of which differs more or less from that of the normal mucous membranes. We may remark, generally, that they are seen rather more frequently at the ex- ‘ tremities of the internal cutaneous system, near its union with the external, in the nasal fossæ, the buccal cavity, the pharynx, the rectum, the uterus, and the vagina. They are not however more common, the nearer they are to the limits of the external cutaneous system ; they are, on the contrary, almost always a little distant from these limits, so that for instance the ' excrescences of the nasal fossae are developed more frequently in the maxillary sinus, those of the buccal cavity in the back part of the mouth, those of the urinary apparatus in the bladder, those of the female genital system in the uterus or in the vagina, and we are mrable to tell to what this peculiarity must be ascribed.

The excrescences'spoken of are termed polypi. They are attached to the internal face of the mucous membranes by a long or short, broad oi narrow peduncle, and are loose in their cavities. Their structure is not always the same. They are generally formed of a very homogeneous substance ; sometimes however we see fibres perpendicular to the substance which supports them. They vary also in consistence, being sometimes hard, sometimes soft and mucous. They sometimes receive a great many very irregular vessels which form

(1) Thomson, Lectures on inßammatwn, Edinburgh, 1813, p. 421, 422.

large elnuses ami have no proper pariet.es, but in others, vessels cannot be distinguished. Sometimes they are very inconvenient from their size and from the compression which they exercise. Sometimes they injure the health by frequent hemorrhages from their surfaces or from their ruptured vessels. Sonretimes they inflame and suppurate. The place where they are developed usually shows a great tendency to reproduce them when they have been extirpated.

Schirms and cancer are also peculiar to the mucous membranes and to the glandular system ; they may be considered as resulting from the development of these membranes. These abnormal productions appear in some parts more frequently than in others, and are generally seen in those where polypi are developed. The parts, however, most frequently affected, are the female genital organs and the rectum ; they also are often developed in some other points, more particularly where polypi rarely grow, as in the pyloric orifice of the stomach.

This disease is unquestionably situated in the mucous crypts, and arises from the frequent irritation of the parts in which it is developed. It often contracts the cavity of the organ, because of the considerable thickening usually resulting from it.

It is rare that the mucous membranes ossify, or that osseous matter is deposited on their posterior face ; but round, fatty tumors are often developed in several places, among others in the esophagus and the small intestine: Monro(l) and Vicq d'Azyr(2) have denied the existence of these bodies, but wrongly ; although other tumors, entirely different in character, may possibly have been confolmded with them.

The general condition of all these anomalies is the increase of the formative power, inflammation, which however often attacks the mucous membranes without giving place to them.(3) One of the most usual consequents of this inflammation, especially when it has continued a long time, is the thickening of this membrane. Ulcers are not unfrequently developed there ; but the mucous membranes can suppurate without ulceration, doubtless on account of the great analogy which exists between their natural secretion and pus. The unattached surface of the inflamed mucous membranes often secretes a greater or less quantity of coagulable substance which gives rise to solid or hollow cylinders. This is seen for instance in croup, {angina membranacea s. jjolyposa.) The parietes of the mucous membranes very seldom adhere after exsudations of this matter, but they often unite after ulcers, especially in those places where union is not impeded by motion and the continual passage of foreign substances.

(1) Encylc. mêth. anat. pathoL, p. 343.

(2) Morbid anat. of the human gullet, Edinburgh, 1815, p. 196.

(3) As the mucous membranes were not considered in a general manner before the time of Pinel and Bichat, we seek in vain in the writings of previous authors for general views of diseases of this system ; but if we reflect that, properly speaking, they form the lungs, the stomach, the intestines, and the appendages of these viscera, we have only to study what has been written on the morbid affections of the latter to have a knowledge of their diseases. The works of Bonnet and of Morgagni contain many valuable facts upon the pathological anatomy of the mucous membranes. Pinel arranges among the inflammations of these membranes all the catarrhal affections of the ancients; or rather he has admitted as inflammations of these organs only the catarrhs (flux sereux, muqueux, &c.) of his predecessors. No one however had treated particularly of the subject when P. A. Prost published his Médecine éclairée par l'observation et l'ouverture des corps, (Paris, 1804, 2 vol. in 8vo.) He there establishes from a great many facts the following propositions : irritation of the mucous membrane of the intestines extends to the animal centre without pain : the excitement, the agitation, the derangement of its functions are relative to the susceptibility of these organs, to the causes which irritate them, to the natural disposition, and to the sensibility of the individual. The alterations of these viscera have more influence on the brain in proportion as their arteries are more developed, the red blood more abundant in their extent, and the means of irritation more active. The pains of the abdomen depend on the state of inflammation of the peritoneum and of the surrounding cellular tissue. Inflammation of the mucous membrane of the intestines, when very active, frequently extends to the peritoneal coat, but the latter naay be inflamed, although the mucous coat is healthy. The prostration of the animal centre results from the absence of red blood from the intestinal mucous surface, whether there be alteration and thickening-, hardness, fungosity, infiltration, ulceration of this membrane, or even if these affections do not exist. Finally, alterations of the intestines with or without inflammation, are in relation with the last symptoms of the animal functions preceding death. Prost could not but deduce from these general facts a medical theory very different from that taught before his time ; but he did not draw from his observations definite conclusions : confined as he was by the despotism of classifications, he made only an indecisive application of them to pathology.

Broussais has gone still farther. After censuring the exaggerations of Prost he concludes by attributing all essential fevers to the inflammation of the mucous membranes, especially those of the stomach. Inflammatory, gastric, bilious, mucous, adynamic, ataxic, and typhoid symptoms result, in his opinion, directly or sympathetically, from this inflammation : no inflammation of any organ whatever can give rise to the symptoms of simple acceleration of the circulation, unless the mucous membranes of the stomach are more or less affected. He ascribes to the acute, chronic, latent, obscure inflammation of these membranes, a host of diseases, as the exanthemata, gout, rheumatism, vesanies. The danger of most acute or chronic diseases arises principally from the inflammation of the mucous membranes which the physician should foresee, prevent, and combat ; finally it is the most frequent and gravest disease, that which affects the rest of the organization in the greatest degree, and a profound knowledge of which is the key to pathology. Broussais has also given a fine history of the inflammation of the pulmonary and gastro-intestinal mucous membranes, and important ideas upon the inflammation of the other mucous membranes. He thinks that all the alterations of texture of which they are susceptible depend on acute or chronic inflammation. However exaggerated these ideas of inflammation of the membranes may be, it is no less true that they are erroneous only in being too general, and that Broussais has supplied a great deficiency in pathology, in pathological anatomy. His opinions and their varieties may be found in the Histoire des phlegmasies, ou inflammations chroniques, Paris, 1808, 2 vol. in 8vo. ; id. 1816, 2 vol. in 8vo. ; id. 1821, 3 vol. in 8vo., in his Examen des doctrines médicales généralement adoptees, Paris, 1821, 2 vol. in 8vo., and in his Annales de la médecine physiologique, Paris, 1822. Boisseau endeavored in 1817 to prove that gastritis did not constitute all essential fevers, and that inflammations of the mucous system were not the only ones which produced fevers. See his Réflexions sur la nouvelle doclrin£ médicale, in the Journal universel des sciences médicales, vol. vii. p. 1, and vol. viii. p. 257 ; his article, Eièvre in the Dictionnaire abrégé des scie?ices médicales; his Pyrétologie physiologique, Paris, 1823, in 8vo. ; id. 1824, in 8vo. — See also Roche, Réfutation des objections faites à la nouvelle doctrine desflevros, Paris, 1822, in 8vo. — Bégin, Physiologie pathologique, Paris, 1821, in 8vo. — J. Cloquet Mémoires sur les ulcérations des intestins, in Nouveau journal de médecine, vol. i. p. 107. — Scoutetten, (De V anatomie pathologique en général, et de celle de V appareil digestif en particulier, Paris, 1822, in 4to.), and Andral, (Alédecine clinique, Paris, 1823, in 8vo.), have carefully described marks of inflammation of the mucous tissue. — Goupil, Exposition des principes de la nouvelle doctrine médicale, avec un PréeU de thèses soutenues sur ses différentes parties, Paris, 1824, in8vo. F. T.

§ 431. Do tho mucous membranes assist, in forming the exanthemata so common in the external cutaneous system, and which appear under such various forms ?(1)

Perliaps upon no question in pathology are there so many different opmions.

Exanthematous diseases doubtless form in the external portion of the mucous membranes near the places where they are continuous with the external cutaneous system when the latter is itself affected. Besides, these membranes frequently inflame with eruptive diseases of the skin. But do the exanthemata assume there the same form as in the common integuments ? The great difference in the texture of the two parts authorizes us to think, that the cutaneous exanthema differs much from that of the mucous membranes, and experience teaches, that in many exanthematous diseases, for instance in small pox, all the mucous membranes are often acutely inflamed, but no pustules are found in them, although they cover the skin. Some observations however, as those of Wrisberg(2) and Blane,(3) estehlish incontestably, contrary to the opinions of the most celebrated physicians, that, when the variolous pustules exist in the skin, they sometimes form also in the mucous membranes, especially those of the air-passages and alimentary canal, and differ but little from those on the surface of the common integuments.

§ 432. The mucous membranes are not unfrequently developed abnormally ; usually, however, after inflammation when it has terminated by suppuration. We think that every suppurating surface may be compared to an imperfect mucous membrane.

After inflammation, the cellular tissue, imbibing the coagulable part of the blood whicli has infiltrated into its texture, changes into a soft and whitish ihembrane, which soon acquires the power of secreting a peculiar fluid, called pus ; so analogous to mucus that we cannot distinguish them by our reagents. This membrane is intimately united to the subjacent cellular tissue and soon receives numerous vessels. Its surface, which is at first smooth becomes uneven, and numerous small tubercles, formed of vessels and cellular tissue, arise ; these are called granulations ; in this state pus is continually secreted, until the number of its vessels diminishes, the granulations waste, and in their place is developed a substance which resembles more or less the natural membrane which previously existed. The mucous membranes then suppurate more readily than all other parts ; and what is more remarkable, they have the power of forming pus, although there is no previous destruction of their tissue and the formation of a new one — indispensable conditions in other organs. The same perhaps is true of the serous membranes : but they then resemble the mucous membranes very much, as is shown by their thickening, softening, the increased number of vessels in their substance, and their consequent redness.

(1) Scoutetten, loc. cit. — Aiidral, loc. cit.

(2) Sylloge comment., p. 62.

(3) 'trans.foT impr. of mcd. and surg. knowl., vol. iii., London, 1812, no. 31, p. 426, W.

The accidental cysts are often similar to the mucous membranes, both in regard to their structure and the nature of the fluid which they contain ; and Bichat has gone too far in referring them all to the class of serous membranes. We have found more than once, in the ovaries and in the uterus, large and small cysts which resemble the mucous much more than the serous membranes. We beheve also there is an exact relation between their structure and the nature of the fluid contained by them, for we have recognized that the cysts filled with serum resemble much the serous membranes, while others filled with thicker mucilaginous or purulent matter are more similar to the mucous membranes.

The purulent cysts, which are connected with the surrounding cellular tissue less intimately than are ordinary abscesses, naturally lead to the latter.

Junk

A. NORMAL STATE.

§374. The cutaneous system {sysiema cwfaneitm) (1) forms a sac which constitutes a general envelop to all the other organs. It may be divided into two large sections, the external and the internal cutaneous system. The former is usually termed the skin (cutis) or the common integuments (tegumenta communia). The second is the system of the mucous membranes (membranæ mucosae). Although they differ much, they are only modifications of one and the same type, as they are uninterruptedly continous with each other and in fact are similar in form, in composition, in qualities, and in functions.

§ 375. The external form of this system is that of a sac turned on itself, andconsequently double. From this arrangement openings are formed both in the upper and in the lower half of the body, by which the external and the internal cutaneous, systems communicate and are continuous with each other.(2) These openings generally lead into the chief portion of the mucous membranes. The latter form a tube which extends the whole length of the head and the trunk, and is called the alimentary canal. This canal, which has appendages in several parts which give rise to most of the viscera, presents above the openings of the mouth and nose, and below that of the anus. This part of the internal cutaneous system extends above the diaphragm into the cavity of the nose and that of the mouth, and also to their appendages, the salivary glands, and continues by the nasal canal, with a small process in form of cul-de-sac, comprising the tunica conjunctiva and the lachrymal ducts. The mucous membranes of the nose and mouth reunite in the pharynx, forming one, which divides lower down into two branches, the anterior for the trachea and the lungs, the posterior for the alimentary canal. The internal membrane of the respiratory system is the largest cul-de-sac presented by the internal cutaneous system at its upper part. The posterior branch gives olF another to the internal ear. Below the diaphragm it furnishes

(1) Willbrand, Das Hautsystem, in alien seinen Verzweigungen, Giessen, 1813.— Hébréard, Mémoire sur l'analogie qui existe entre les systèmes muqueux et dermoïde, in the Mém. de lasoc. méd. d'émulation, vol. viii. p. 153.

(2) A. Bonn, De continuationibus membranarum, 1763.

308

GENERAL ANATOMT.

new culs-de-sac, which ramify, and extend to the liver and pancreas. Forming then the most internal layer of the alimentary canal, it terminates in the anus, where it is continuous with the external cutaneous system.

Besides this general internal cutaneous system, we find others also, both in the upper and the lower parts of the body, which only represent branches of the culs-de-sac ; these are, 1st, the internal membrane of the meatus auditorius externus ; 2d, that which covers the internal face of the eyelids, the anterior face of the eye, and the lachrymal ducts ; 3d, the mammary glands ; 4th, the mucous membranes of the genital and urinary systems, which commence by a common opening.

It is impossible to overlook the gradation which exists from the absolute insulation of some parts of the internal cutaneous system, to its perfect union in a single organ. The general system of the mucous membranes of the upper and lower parts of the body, of which we can in imagination place the origin in the mouth and intestinal canal, forms an uninterrupted cavity. That of the eye communicates with it only by a narrow channel, but is not insulated from it, unless after leaving the class of reptiles. That of the mouth and of the meatus auditorius externus are connected with each other in the membrane of the tympanum, but they do not form one cavity. Thé membrane between the orifice of the genital . organs and the anus so much resembles a mucous membrane in its softness and its abundant secretion that we are almost authorized to say it unites the two openings, and really blends them in one. Finally, the mucous membrane of the mammary glands is the only one which is wholly distinct from the general internal cutaneous system.

§ 376. The whole cutaneous system is then formed of two large canals, one narrow and provided'with appendages in form of culs-de-sac, the intestinal canal ; the other broader, the common integuments, which also possesses some processes in cul-de-sac, which proceed internally. It every where presents two surfaces, one of which is loose, the other adherent. In the common integuments, the loose surface is external, and the other internal ; the contrary is the case in the mucous membranes. Thence it follows that we may consider the two sections of the system as two canals, one of which would be folded on itself.

The internal face of the cutaneous system is attached directly or indirectly to the muscles by a short cellular tissue. With the external system this union is generally direct ; for the aponeuroses are almost always interposed between the muscles and its internal face, so that the functions of the muscles it covers are rarely in relation with its own. With the internal system, on the contrary, it is direct ; for the mucous membrane is separated from the muscular membrane only by cellular tissue, which is the same as itself in regard to structure and functions,. The external cutaneous system envelops the voluntary muscles ; the internal circumscribes most of the involuntary or hollow muscles.

OF THE CUTANEOUS SYSTEM !N THE NORMAL STATE. 309

The loose surface of the cutaneous system everywhere forms folds, projections, and depressions of different kinds, which increase its extent more or less permanently.

§ 377. In considering the cutaneous system as a sac folded several times on itself, we do not propose to give a history of the origin of the different parts of the skin, nor to pretend that the different excavations are hollowed from without inward, in the midst of a mass which is at first solid and homogeneous, so that the upper and lower cavities of the intestinal canal meet half-way, while the others not extending so far would still preserve their appearance of cul-de-sac. There are some facts which seem to favor this hypothesis. Thus the openings do not at first exist, until about the sixteenth w-eek of uterine existence, and the upper and lower portions of the intestinal canal which are separated from each other not unfrequently form a cul-de-sac, each on its side, But these phenomena do not prove that the internal portions of the cutaneous system arise from the prolongation of the external inward. We can also explain satisfactorily the non-existence of openings in the commencement without having recourse to this hypothesis, and by admitting that the skin gradually tears in the place where they exist by the progress of the formation of the cavities proceeding from within outward. This manner of viewing the subject appears more accurate than the other, since in regard to the second argument favorable to the latter ; 1st. The place where the separation exists between the upper and the lower extremities of the intestinal canal is not always the same ; being often situated in a very distant part ; it is usually connected with one extremity only, mo.st frequently the lower, and consequently in this case it would follow that the internal portion of the skin is not developed except from a single opening. 2d. The upper and the lower extremities not unfrequently do not exist, and we find several perforations along the passage of the internal portion of the skin. 3d. The same arrangement is observed in other processes of the skin, terminating also in cul-de-sac, as in the urinary apparatus and the genital system, where, if we except the closed extremity, the extent of which is frequently considerable, it not unfrequently happens that the internal and tire external parts are perfectly developed, while, according to the above mentioned hypothesis, their formation should have been arrested where the intermediate partition exists. It is more correct then to admit that the internal part of the skin is formed from within outward ; that it probably takes its departure from several different points ; that these join as they are developed and then unite to the common integuments, making wnth them an entire whole.

§ 378. The cutaneous system is essentially composed of several layers which may be considered as so many separate systems or only as the different parts of the same system. It seems more convenient to follow this latter method, because by it we arrive at a better knowledge of the whole system. These different layers are, 1st, the derma (derma, corium) ; 2d, the papillary tissue (textus papillaris) ; 3d, the rete mucosum [rete Malpighii) ; and 4th, the epidermis (cvticula.)

310

GENERAL ANATOMT.

Bichat has separated the epidermis from the skin, and has considered as separate systems several parts described by us (§ 16) as appendages to the epidermoid system ; but they are so intimately connected with each other, so identified in different parts, that it does not seem proper to insulate them. We may then consider all these layers generally in the whole cutaneous system, and then particularly in each of its two sections.

§ 379. The derma is the strongest, the firmest part, and the base of the whole cutaneous system. Always united to the adjacent systems, it adheres to the muscles, in the external skin by its internal face, and in the internal skin by its external face. It is white, soft, of variable thickness, having but few vessels and nerves, elastic, capable of contracting and extending to a considerable extent ; it does not possess a high degree of vitality and when destroyed is not reproduced. Its consistence and thickness in different parts of the body vary very much : generally speaking they are greater in the external than in the internal cutaneous system.

§ 380. The papillary tissue {textus papillaris) which is applied to the loose surface of the dermis is in reality only a greater development of it, being composed of mucous tissue, of vessels, and of nerves ; it has the form of small, regularly arranged tubercles which vary extremely in the different parts of the cutaneous system in volume and form. These tubercles increase the extent of the system still more than the folds (§ 377) which support them. The extreme sensibility of the cutaneous tissue depends upon them.

§ 381. The rete mucosmn {rete Æalpighii) is a mucous and semifluid substance having an immense number of capillary blood-vessels. It is more readily distinguished from the papillary tissue and the epidermis in the external than in the internal cutaneous tissue. In this tissue and in the preceding the processes of nutrition take place most actively.

§ 382. The epidermis {epidermis, cuticula) is whitish, solid, brittle, without vessels or nerves, and entirely insensible. It receives a perfect impression of all the irregularities of the layers which it covers. We cannot always insulate these latter in the internal cutaneous system. It becomes much thicker by friction, and is reproduced entirely after being destroyed.

§ 383. We also find in several parts of the cutaneous system simple glands, a species of round bursæ, which vary in size and are called in the internal cutaneous system, the mucous glands or crypts {glandulæ s. crypto?, mucosæ), and in the skin are termed the sebaceous glands {glandtdœ sebaceœ).

§ 384. In those parts where the external and the internal cutaneous systems are continuous with each other, the former becomes thinner, smoother, finer, and sometimes redder than usual, as in the lips. The general characters marking the commencement of the latter are, that the epidermis is more easily detached from the subjacent layers than in the rest of its extent.

OF THE CUTANEOUS SYSTEM IN THE ABNORMAL STATE. 31

§ 385. The cutaneous system envelops all the other organs and forms an entire whole ; but at the same time it connects the organism directly with external objects, for it continually absorbs materials from without and expels them within ; it establishes a limit, a sort of bridge between the individual organism and the rest of nature. It is in fact the most important part of all the organs of the nutritive hfe. Hence the frequerit diseases in this system and its great influence on the general health, and the part it takes in all the changes which supervene in the organisation ; hence, also, the close sympathy between all its parts, both in the healthy and the diseased states.

§ 386. The cutaneous system diflfers in the sexes : it is much thicker, firmer, harder, and less sensible in the male than in the female. It varies at different periods of life, as follows ;

1st. It is less extensive in the early periods of existence, not only from the deficiency of some parts, as the extremities, but the intestinal canal is shorter and narrower, and the folds appear late.

2d. It varies in form. At first both the intestinal tube and the anterior part of the body is open ; there are not two canals opening into each other, but only two semi-canals.

3d. There are at first more vessels and nerves, whence the process of nutrition is then carried on more actively.

4th. It is much thinner in the early periods of life ;

5th. It is then more loosely united to the subjacent parts ; and,

6th. There is more analogy between the internal and the external portion.

B. OF THE CUTANEOUS SYSTEM IN THE ABNORMAL STATE.

§ 387. The cutaneous system reproduces itself after having been destroyed, but not perfectly : hence we can always distinguish cicatrices from the true skin. We shall enter into more details upon thk subject when treating particularly of the external and the internal cutaneous systems.

§ 388. The congenital deviations of formation in this system are either its total deficiency or that of some of its layers, and its superabundance, as seen in the formation of abnormal appendages. The accidental anomalies of formation, if we except mechanical injuries, almost always result from alterations in texture, to which the cutaneous system is very subject, because of the circumstances mentioned above (§ 385). Beside those diseases in which it participates with other parts, it is often the seat of acute or chronic inflammation. Accidental tissues are frequently developed either in its proper substance or in the subjacent mucous tissue. Other alterations in its texture, for instance ossification, are rare.

Si2

tENERAL ANATOMY.

ARTICLE SECOND.

SPECIAL REMARKS ON THE EXTERNAL CUTANEOUS SYSTEM.

A. OF THE EXTERNAL CUTANEOUS SYSTEM IN THE NORMAL STATE.

I. OP THE EXTERNAL CUTANEOUS SYSTEM IN GENERAL.

§ 3S9. The external cutaneous system(l) or the pïoper skin (cutis) envelops the external surface of the wholebody and forms a close sac which possesses its exact form, and is continuous Avith the internal cutaneous system in those parts previously mentioned (§ 375). The skin differs from the internal cutaneous system generally, in being thicker, firmer, dryer, and less vascular. As we have already remarked generally on its form and composition, we have only to describe its component layers.

§ 390. The derma (corium. derma) is a white, solid, and dense tissue, which differs in several respects.

Generally considered, it is composed in great part of layers which are very distinctly seen on its internal face and after maceration. These layers are produced by a substance very analogous to fibrous tissue;(2) their direction is oblique from within outward: they are also narrower on their external than on their internal face, and the vessels, the nerves, and the hairs pass through the former. This laminar tissue is continuous in many places, for instance, in the nucha, the back, the abdomen, the sole of the foot, the articulation of the hand, and in that of the foot, with the subjacent fibrous tissue which it resembles almost entirely, in the palm of the hand and in the sole of the foot, by its shining and evidently fibrous texture. But in most of the cutaneous tissue, especially the trunk, and in all parts of the limbs, its fibrous structure is less apparent and its connections with the subjacent tissue less intimate. We find no trace of fibres in the derma of

(1) In addition to the works which have been quoted, we refer to Malpig-hi, De externo tactus organo, in Epist., London, 1686, p. 21-23. — Hoffmann, De cuticulâ et cute, Leipsic, 1687. — Limmer, De cute simulque insensibili transpiratione, Z,erhst, 1691. — A. Kaaw, Perp. Hipp.sic dicta, Leyden, 1738. — F. D. Riet, De organo tactus, Leyden, 1743. — J. Fantoni, Dc curp. integumentis, in Dies, anat.' VII. renov., Turin, 1745, n. i. — Lecat, 'Traite des sens, Amsterdam, 1744. — Cruikshank, Experiments on the insensible perspiration of the human body showing its ajfnity to respiration, London, 1795. — C. F. Wolff, De cute, in N. C. Petrop., vol. viii. — G. A. Gaultier, Recherches sur Porganis. de la peau de l'homme, et sur les causes de sa coloration, Paris, 1809. — Id., Rech, sur l'org.cutané,'t?a.r\s, 1811. — J. F. Schroeter, Das menschliche Gefühl oder organ des Getostes nach den Abbildungen mehrerer herümhten Anatomen dargeslcllt, Leipsic, 1814. — Dutrochet, Observations sur la structure et la régénération des plumes, avec des considérations sur la composition de la peau des animaux vertébrés, in Journal de physique, May, 1819. — Id., Observations sur la structure dc la peau, in Journal complémentaire, vol. v.

(2) Osiander, from observations on the skin of the abdomen of women who died

in child-bed, asserts that the fibre which forms the dermis is distinctly muscular on the internal face of the skin. F. T.

OP THE EXTERNAL CUTANEOUS SYSTEM IN THE NORMAL STATE. 313

the back of the hand, of the sole of the foot, of the forehead, of the scrotum, of the labia pudenda, and of the penis, "when the substance is perfectly homogeneous.

The dermis varies much in thickness. It is undoubtedly thickest on .the back of the hand and in the sole of the foot, and thinnest on the eye-lids, in the mammae of the female, in the scrotum, the labia pudenda, and the penis. It is thinner in the upper than m the lower extremities, and is thicker and firmer on the skull than on the face.

The dermis under the nails presents a peculiar arrangement, which we shall mention when speaking of these last, because all the layers of the skin are jointly modified in them.

§ 391. The skin is often wrinkled or folded, which depends on the different states of extension or contraction of the, sl^i and subjacent parts, or on other causes.

The folds of the first kind are produced by the action of the muscles or by the diminution of fat below the skin in aged persons, and because of its slight degree of elasticity. In fact they result from the circumstance that certain muscles directly beneath the skin, or at least their tendons, act frequently wliile the sldn is not sufhciently elastic to contract and to dilate m the same proportion, or because this membrane becoming still less elastic in advanced age does not contract, while the fat which distended it is absorbed, and it is therefore folded or wrinkled.

Other folds depend on the papillary tissue of the skin. They are very regular, small, compact, and curved. They are very manifest in the palm of the hand and in the sole of the foot. Each of these folds is composed ultimately of two others, for normally their upper face is sHghtly depressed, and the adjacent folds are separated from each other by deeper furrows.

§ 392. Below the dermis, in the panniculus adiposus which it covers, wind a great many subcutaneous vessels {vasa subcutanea) : of these the veins are very considerable, and are always broader than the deepseated veins. From these cutaneous vessels arise those which are expanded in the substance and on the surface of the dermis, most of which only pass through it to be expanded in the latter, so that the tissue of the skin is not very vascular. The same is true of the nerves.

§ 393. In some places, for instance at the commencement of the meatus auditorius externus, at the end of the nose, at the edges of the eyelids, around the anus, the vulva, and the nipple, are considerable openings from whence comes an oleaginous fluid which hardens quickly. These openings lead into small culs-de-sac called the sebaceous glands {glandidÅ“ sebaceæ). As the whole skin exhales an analogous substance, we might be led to think that these glands exist every where ; but it is impossible to demonstrate tliis. Probably the bulbs of the hairs should be considered as organs corresponding to them in structure and in functions (§ 410), or rather we must regard these glands as enlarged bulbs of the hairs which are more developed, since

VoL. I, 40

314

GENERAL ANATOMV.

no hairs come from them, and they are found exactly on the common borders of the external and of the internal, cutaneous system. It would seem also to result from this, that the development of mucous crypts in the internal cutaneous system corresponds to that of the hairs and the epidermis in the external cutaneous system.

§ 394. The papular u lissm {lexlus papillaris) {1) of the skin is composed of small processes situated on the external surface of the dermis, particularly on the elevations of the second kind which this latter presents ; these processes are called papilkc of touch {papillÅ“ iactiis). Each elevation presents two ranges of these papillæ, which however are so connected with each other that they may be considered as forming but one. Like the eminences on the surfaces of which they are seen, they are vei^ manifest in the palms of the hands, in the soles of the feet, in the in the glans penis,(2) and in the mammæ.(3) Their surface is villous. In all other parts they are less distinct, even when the epidermis is removed. Even in the preceding regions we finä none between the elevations in which the papillæ of touch are situated.

The latter are composed of nerves and of fine branches of the cutaneous vessels. According to Gaultier, they principally give the color to the sldn. But this anatomist seems to have confounded them with the vascular tissue which covers them.

§ 395. The external face of the dermis and of the papillary tissue is covered with a fine vascular network, composed ofnumerous central points united' by many anastomosing vessels which are very apparent and regularly arranged.

§ 396. Proceeding from within outward, we find next to the dermis the rete mucosum, or the rete UWalpighii, a mucous homogeneous substance which may be divided into two or three separate layers. (4) It has no openings v/hich allow the papillæ of touch to communicate with the epidermis, but only depressions which correspond to them, and within which they are imbedded as in so many sheaths. This layer is the principal seat of the color of the skin, since in the negro the dermis is as white as in the European, (5) while the rete mucosum always presents the peculiar color of each race. Usually it is considered single, but we have reason to think it compound. Gaultier assigns to it three layers, the first two of which he calls the internal and the external tunica albuginea {tunica albuginea interna et externa)^ because of their color, while he calls the third the hroim substance^ in the negro, where it is very apparent. Of these three layers thé inter (1) Hintze, De papillis cutis tactui inservientihuSy'Leyde.rt, 1747.

(2) B. S. Albinus, De integumentis glandis penis ; loc. cit., lib. iii. c. ix.

(3) B. S. Albinus, Depapillis mammÅ“ et papülæ muliebris ; loc. cit., c. xii.

(4) B. S. Albinus, Quœdam de modis quibus culicula cum corpore reticulari de cuti abscedit, in Annot.-acad., Leyden, 1754, 1. i., c. i. De cognatione et distinctione cuticulæ et reliculi, ibid. c. ii.—De reliculi foveolis vaginisque quibus papillæ continentur, ibid. c. iii. — Nonnulla de usu ct ralione reticuU et cuticulæ, ibid. c. v.

(5) B. S. Albinus, De sede ct causa coloris Æthiopum et ceierorum hominum,Lcyden, ,1737.

OF THE EXTERNAL CUTANEOUS SYSTEM IN THE NORMAL STATE. 315

nal is the thickest and the external is thinnest : both are white ; the middle is colored, but less so than the vascular tissue, so that it cannot be regarded as the principal seat of color except in the negro. Cruikshank has found between the dermis and the epidermis of a negro, who died from small pox, fom* layers besides the papillary tissue ; the internal very thin, a second in which the variolous pustules were developed, a third which was thicker, the proper seat of color, finally a fourth which was whitish, and which he considered the external layer of the third. • This description agrees pretty well with the preceding.

The layers, situated between the papillary tissue and the epidermis, which form this membrane, usually remain united to the epidermis when the latter is separated by putrefaction or boihng ; but they sometimes adhere to the dermis.

§ 397. The epidermis, or cidicle {epidermis, cuticida),{l) is a membranous, homogeneous, thin, semi-transparent expansion, whitish in the European, light gray in the negro, forming the most external layer of the skin, covering the internal layers in every part, and adhering to them intimately. It- thus presents the same folds and thé same inequahties as the latter, and we see on its internal face round depressions which correspond to the papillæ of touch. Its external face is smooth, while the internal is very uneven ; it is finnly united to the subjacent layers ; but ha certain cases this union is entirely destroyed either during life or after death : it seems to take place by numerous small filaments(2) which are perceived very distinctly in the palms of the hands and in the soles of the feet, if the skin be immersed into boiling water, and the epidermis be detached from the dermis. It is however dithcult to determine the nature of these filaments. Bichat considers them as the extremities of the absorbent and exhalent vessels;(3) but we have never been able to fill them, even when the cutaneous vessels had been perfectly injected ; and Hunter has succeeded no better than ourselves. Might they not have been produced from the mucous tissue by the process of boihng ? And if this be false, are they really hollow ?

The same uncertainty exists whether the epidermis be filled with holes called pores, or whether it be only thinner in those places where these pores seem to exist. Many observers, as Leuwenhoeck(4) and Bichat, particularly the former, admit that the epidermis is porous, and Bichat asserts that the oblique direction of these pores alone prevents

(1) C.G. Ludwig-, Decuticulâ, Leipsic, 1735. — Fabricus ab Aquapendente, De totius animalis integumentis, ac primo de cuticulâ et iis quœ supra cuticulâ sunt, in 0pp. omn., Leipsic, 1687, p. 438-452. — J. F. Meckel, De la nature de l'épiderme et du réseau qu'on appelle malpighien , in Mêm de Berlin, 1753, p. 79-97 — Id., Nouv. obs. sur l'épiderme et le cerveau des negres, ibid. 1757, p. 61-71. — B. S. Albinus, De incisuris cuticulæ et cutis; loc. cit., c. iv. — A. Monio, De cuticulâ humanâ, in IlbrA-s, Edinburgh, 1781, p. 54. — J. T. Klinkosch, De verâ naturâ cuticulæ et ejus régénératione, Prague, 1771. — Herman!, De verâ naturâ cuticulæ ejusque regeneratione, Prague, 1775. — Mqjon, Sull' epidermide, Genoa, 1815.

(2) Hunter, Med. obs. and inq., vol. ii. p. 52, 53, tab. 1, fig. 1, 2.

(3) Gen. Anat. vol. iii. p. 351.

(4) Arcan. nat. ep. phys., 43.

316

GENERAL ANATOMY.

them from being seen. Others, on the contrary, as Meckel(l) and Humboldt,(2) deny the existence of these pores. We have never been satisfied of the presence of these openings, and their existence is not necessary, since the exhaled fluids can escape very well through the thinner parts of the epidermis.

The thickness of the epidermis is nearly uniform, except in the palms of the hands, and particularly in the soles of the feet, where it is thicker. In fact, friction increases its thickness, and renders it callous in those two parts ;(3) but that this difference has not entirely a mechanical origin, is proved by the greater thickness of the epidermis of the palm of the hand and sole of the foot even in the fetus(4). This is the reason that it is more difficult to detach it from the subjacent layers in these two parts of the body.

The epidermis is usually formed of one layer only ; but we observe several which are very distinct in those parts where it is thickest. We have observed this several times in the palm of the hand and in the sole of the foot.

§ 398. The epidermis is essentially only the rete mucosum coagulated and hardened. It belongs then properly to the mucous tissue. It is entirely destitute of nerves and vessels, and is consequently dry and insensible. It is completely regenerated by the drying of the rete mucosum. The appearance of the vascular structure presented by it depends either on some extravasation or on the adhesion of a portion of vascular tissue. It has no power of contraction, and but a slight degree of extensibility

The epidermis moderates in part the impressions made on the papillæ of touch in the skin, and in part opposes evaporation. Hence a blister not unfi'equently causes all the serum of the mucous tissue in dropsy to escape in a short time. Hence too the skin not only dries ra.pidly in those parts where the epidermis has been removed either before or after death, but it also adheres intimately to the subjacent organs, while that of the adjacent parts which has preserved its epidermis always remains moist.

That the epidermis arises from the hardening of the rete mucosum is proved by the fact that it is partly the seat of color in the skin, for it always presents the same tint as the rete mucosum, but it is less distinct.

§ 399. The epidermis appears early ; it is already seen distinctly in the fetus of two months ; it is then even proportionally thicker. Besides, the considerable growth of hairs and the formation of the caseous substance {vernix caseosa) with which the skin of the fetus is covered, prove the great activity of the epidermoid system at this period.

We may state, as sexual differences, that it is softer and thinner in the female than in the male.

(1) Mérti. de Berlin, 1763, p. 63.

(2) Uebcr die gereizte Muskel- und Nervenfaser, vol. i. p. 156.

(3) Nürnberger, De cuticulae frictione cowprimentc callosä, Wittenberg, 1789.

(4) B. S. Albinus, De sede col. cutis, p. 9. _ •

OF THE EXTERNAL CUTANEOUS SYSTEM IN THE NORMAL STATE. 317

The races of the human species also present some differences. Although several anatomists, among others Malpighi(l) and Littre,(2) affirm it is white in the negro, we now know that it has a grayish, brownish tint. We agree with the opinion of Santorini,(3) Ruysch,(4) Albinus, (5)Meckel,(6) and SÅ“mmening.(7)

It is a little coarser in the negro than in the European.

II. OF THE MODIFICATIONS OF THE EXTERNAL CUTANEOUS SYSTEM, OR OP THE APPENDAGES OP THE SKIN, THE HAIR, AND THE NAILS.

§ 400. The hairs and the nails are generally considered only as appendages of the epidermis. But in our opinion this is incorrect ; for the nails and the hairs are in fact modifications of the whole cutaneous system, although the epidermoid system and that of the rete mucosum predominate in the most of then length. In fact the dermis below the nails is peculiarly modified, and corresponding variations are observed in the other layers of the skin. We must then consider as belonging to the nail not only the epidermis which is particularly modified, but also the whole cutaneous texture. The same is the case with the hah, for their bulbs are evidently, analogous to the dermis.

1st. Of the nails.

§401. The epidermoid portions of the nails, or the proper nails (ungues), (8) are broad, hard, shghtly convex, and oblong layers formed at the ends of the backs of all the fingers and toes, and which cover the anterior part of the thhd phalanx, projecting forward and on the two sides.

We distinguish in the nails three portions, the posterior or the root, the central or the body, and the anterior or the free extremity.

The root (radix unguis) is concealed under the skin, and is softer and thinner than the other two parts. It gradually becomes thinner, and terminates in a rounded edge. It is one fifth or one sixth of the whole length of the nail. The central part, the body, is much larger than the other two parts, and its internal face adheres intimately to the skill, while the external face is unattached. Its posterior part varies proportionally in extent according to the subjects, and almost always diminishes from the thumb to the fifth finger : it is white, convex forward, and concave backward, and is termed the crescent (lunida).

(1) Exerc. dc externo tactus organo.

(2) Hist, de I'ac. des sc. de Paris, 1702, no. 13, p. 40.

(3) Observ. anat. Venet. 1724, 1. i. p. 1.

(4) Curæ renovatæ, no. 59, 87.

(6) hoc. cit., p. 6.

(6) Mêm. de Berlin, 1753, p. 93.

(7) lieber die körperlichen Verschied, des Negers vom Europrœ, lT85, p. 45.

(8) Frankenau, Z)e unguibus, Jena., 1696.— Ludwig“, De ortu et structura unguium, Leipsic, 1748. — B. S. Albinus, Deungue humano ejusque reticulo, itemgue de cutis loco, qui unßue tactus ac de loci istius papillis, in Annot. acad. vol. ii.-xiv. — De natura unguis, ibid. c. xv. — Bose, De unguibus humanis, Leipsic, 1773.— Haase, De nutritions unguium, Leipsic, 1774.— Nürnberger, Meletemata super digitorum unguibus, Wittenberg, 1786.

318

GENERAL ANATOMY.

The anterior is much greater, and appears reddish. The/ree exlremiiy projects beyond the skin, so that its two faces are entirely free. It is tire thickest part of the nail, which consequently diminishes gradually in thickness from behind forward. The length of this extremity is not fixed, and depends on the greater or less degree of attention with which it is cut. Left to itself,- it becomes very long, thick, and pointed.

§ 402. The nails are connected only with the epidermis, and adhere to it so intimately in all their circumference that they are retained firmly in place. The nail ig sbghtly covered behind and on the sides by the epidermis which is reflected forward from below. Behind, this membrane projects on the concave and thin edge of the skin wdiich covers the posterior part of the nail, forms a small groove often separated from the skin by a kind of channel, and which is intimately connected before with the anterior edge of the crescent. Thence the epidermis goes backward, insinuates itself below the portion of the skin which slightly projects above the nail,is reflected on the inferior face of the nail, and is continuous with it forward. On the sides, the epidermis projects as it does behind, but it is not extended foward, and is also continuous with the edge of the nail. The epidermis having covered the anterior extremity of the finger 1-eaves the skin, and attaches itself to the anterior convex edge of its central and adherent part, and blends itself with its substance.

Thus, the nail (in the common sense of the word) is only a thickened portion of the epidermis, which detaches itself, like this latter, from the subjacent layers of the skin.

§ 403. But these subjacent layers present of themselves some modifications. The dermis is thicker, softer, has no layers, and is not attached to the nail by any prolongation. Under the body of the nail, it is very red and more vascular than in the other parts. Under the root and the crescent, on the contrary, (if we except the nails of the toes, which usually have no crescent,) it is white, so that the whiteness of this semilunar spot does not depend on the nail, but on the skin. Its upper face has very distinct longitudinal fibres, especially in its reddish anterior portion, which is the most extensive. These fibres may be compared to the papillœ of touch, and the internal and inferior face of the nail, which is soft and also provided with very distinct longitudinal fibres, may be compared to the rete mucosum intimately connected with them. In the small nails of the toes, which are imperfectly developed because they are compressed, we discover neither the fibrous structure of the skin nor the rete mucosum, but the projections and excavations which correspond to them are irregular and more similar to papillœ.

§ 404. The epidermoid portion of the nail is composed of superimposed layers, the external of which extends the whole length, while the internal gradually diminish from behind forward, so that the most anterior are the shortest ; these, too, are also the softest, and become, at least apparently, more fibrous. The structure of the nails is homogeneous, like that of the epidermis ; they have neither vessels nor nerves.

OF THE EXTERNAL CUTANEOUS SYSTEM IN THE NORMAL STATE. 319

§ 405. The epidermoid portion of the nails presents no trace of sensibility or contractility. The vital phenomena which take place in them are very slow, except the acts of growth, which proceed rapidly, as is proved % their continual increase. § 406. The nails begin to appear in the fifth month of fetal existence, and are very imperfect at the ninth.

2d. Of the Hairs.

§ 407. The hairs {pili, crines){l) are filaments of various lengths, always thin in proportion to their length, about g-i-g- of an inch in diameter, more or less cylindrical and usually smooth. We rarely 'perceive at intervals these swellings, which are apparently produced by some disease. Their attached extremity, called the bulb {bulbiis,) is a little thicker and always soft, the other is slightly pointed. In the normal state, they are seen only on the external cutaneous system, or the skin properly so called, covering all its parts, except the palms of the hands and the soles of the feet, where it is very remarkable that that the epidermis is considerably thick. We must remark in general,

1st. That principally around these points where the external cutaneous is continuous with the internal cutaneous system, we find numerous hairs, which assume a peculiar arrangement, as on the edges of the eyelids, in the nostrils, at the entrance of the ears, around the mouth, the anus, the vulva, and the mammæ.

2d. That the law of polarity exists between the parts on which they grow in abundance ; as in the head and the pubis, on the chin and the anus, on the back and the belly.

§ 408. The hairs are composed of two substances, an external and an internal.

The external., which surrounds the other like a sheath, has all the properties of the epidermis. It is always transparent, white, and very difficult to destroy ; it is continually reproduced, and in the bulb or follicle is more or less evidently composed of several layers.

Under this sheath we find a colored substance formed of about ten filaments, probably vessels. The form of this substance resembles that of the hairs, but it is much thinner than the internal envelop. It is imbedded into the centre of a fluid, which being partially lodged in

(1) P. Chirac, Lettre écrite à M. Regis sur la structure des cheveux, Montpellier, 1668. — Malpighi, De pilis observationes ; in Opp. posth., London, 1697, p. 93-96. — M. J. J. Bajerus, De capillis diss., Jena, 1700. — O. Zaunslifer, Diss. exhibens historiampilorum in homine, Leyden, 1738. — Meibomius, Depiiis eorumque morbis, Helmetadt, 1740. — G. A. Langguth, De pilo parte corp. hum. non ignobüi, Wittenberg, 1749. — P. Grutzmacher, De humore cutem inungente, Leipsic, 1748.— e. P. L. Withof, Anatome pili humani, Duisburg, 1750, in 4to. — J. H. Kniphof, De pilorum usu, Erford, 1754. — J. P. Pfaff, De varietatibus pilorum naturalibus et prÅ“ter naturalibus, Halle, 1799. — Rudolphi, De pilorum structura, Gripswald, 1806. — Grellier, Dissertation sur les cheveux, Paris, 1806. — Rudolphi. Auf satz über Hornbildung ; in Aèhandlungen der Wissenschaften von Berlin, 1818, p. 180. — Rowland, An historical, philosophical, and practical essay on the human hair, London, 1818' — Buek, Diss. de pilis eorumque morbis, Halle, 1819.— Aegidi, Dissertatio de pilorum anatomiâ, Berlin, 1819. — Hensinger, Remarques sur la formation des poils, in Journal complémentaire du Diet, des sc. mêd., vol. xiv., p. 229. — Id., Sur la régénération des poils, same journal, vol. xiv., p. 339.

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GENERAL ANATOMY.

the canal formed by the filaments jxirtly scattered between theîn and the external envelop, unites them together, and constitutes, with them, the marrow of the hairs.

This internal substance corresponds undoubtedl.y to the rete mucosum of the skin, and is the coloring matter of the hairs, which whiten when it disappears.

§ 409. The hairs do not seem to receive blood-vessels, at most we can perceive but a few, and these very seldom, in the inferior swelled portion of the bulbs, which is provided with one or more openings. Through these come the blood-vessels, and probably the fine nervous filaments. In fact we cannot plainly distinguish the nerves, but the analogy derived from the coarse hairs of animals and the pain occasioned by their removal, authorize us to suspect their existence. It is, however, certain that the nerves do not extend beyond the bulb.(l)

§ 410. The hairs are situated under the skin in the mucous tissue, which is almost always filled with fat. The largest are found there, (although this arrangement is not so apparent in regard to the smaller ones,)in the small, closed, thin, whitish and very vascular envelopswhich loosely surround them, pass through the openings in the dermis (§ 390), thus arrive at the epidermis, continue with it, remain fixed to its internal surface as small hollow prolongations, when it is detached from the dermis. There is no adhesion between the hairs and the envelops except at the extremity of the bulb, so that in this place the hairs appear more or less villous on their surface. A thin fluid exists betvmen them and the surrounding sac, which in the dense hairs of animals is real blood.

§411. From the want of nerves, the hairs are insensible. They have no contractile power ; but the formative power is much developed. They grow constantly, and lengthen even after death, or when detached from the body. (2) Thus they are reproduced after having been lost from accident, but not when vitality is absolutely extinct. They possess great strength, and are with difficulty destroyed, undoubtedly because of their external envelop.

§ 412. According to the latest researches of Vauquelin,(3) the hairs are cemposed,

1st. Of an animal substance which constitutes their base, and is very similar to dried mucus, and certainly comes from the external envelop.

2d and 3d. Of two oils, one white and concrete, the other blackish, on which their color depends, at least in part, and which undoubtedly belong to their internal substance, since they vary according to the color of the hairs, and are not colored in those which are white.

4th. Of iron.

5th. Of a little of the oxide of manganese.

(1) Rudolplii has followed the nerves into the bulbs of the mustaches of the seal — ag has also Andral, jun. See his note : Sur les nerfs qui se rendent aux mustaches du phoque ; in the Journal de physiologie expérimentale, vol. i., 1821, p. 73. F. T.

(2) Krafft, in Nov. corn. Petrop., vol. ii., p. 24.

(3) Annales de chimie, 180Ö, vol. Iviii.

OF THE EXTERNAL CUTANEOUS SYSTEM IN THE NORMAL STATE. 321

6th. Of the phosphate 7th. Of the carbonate

I of lime.

8th. Of silex.

9th. Of a considerable quantity of sulphuf § 413. The hairs differ from each other very much in the different regions of the body. The hairs of the head {coma s. capilli s. cœsaries) are the longest, the strongest, the most numerous, and the closest

Next come those of the beard, the hairs of which are distinguished from those of the head in being more distant from each other.

Next come those of the pubis, of the axilla, of the anterior face of the thorax, and of the abdomen, the eyebrows, the eyelashes, the hairs found in the nose, the anus, and those on the limbs, which become shorter and thinner as we descend to the lower part of the limb, and finally, those of the cheeks and the forehead.

The hardest and coarsest are those in the nose, and those on the face are, if we except the beard, the softest. The hairs of the pubis are the thickest ; next come those of the axilla, then the hairs of the head, next the eyebrows and the eyelashes.

The color of the hairs is usually the same in all parts of the body, but to this rule there are many exceptions. It sometimes happens, but it is rate, that a part of the hairs of the head are unUke the rest in color, more often, even usually, only some hairs are discolored, while the rest preserve their primitive color.

All the hairs of the same subject do not appear at the same time. The hairs of the head exist at birth, while the beard and the hairs on the pubis and the axilla do not appear till puberty.

§ 414. The hairs are subject to very considerable periodical changes.

The ‘skin is entirely smooth till towards the middle of fetal existence. At this time, however, it is covered with numerous short fine hairs, a kind of down {lanugo). At first these hairs have no color, but assume one as the period of birth approaches. On certain parts of the body, for instance, on the face, they are much longer than the permanent hairs which afterwards appear in these same parts. Their length is at first almost equal m every part, but at birth however, those of the head are much longer and stronger than the rest.

These downy hairs of the fetus fall some before, but most of them after, birth. They are found in the waters of the membranes and in the meconium. Those which replace them on the body do not begin to appear till puberty, when the beard and the hairs of the pubis, of the axilla, and of the trunk are developed. The hairs of the head, on the contrary, remain the same and grow much more rapidly after birth than before.

The color of the hairs generally becomes deeper in age : this rule is, however, subject to exceptions, although they are few.

Sooner or later, usually about the age of thirty, the hair begins to whiten, by the disappearance of the internal substance. A little later when the external envelop has continued for some time to grow regu

of all.

VoL. I.

41

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GENERAL ANATOMY.

larly, the attachments existmg between it and the follicle in which it is contained are destroyed, and the hair begins to fall otf.

The white hairs contain a colorless oil and some phosphate of magnesia, which is not found in the colored hair.

Both of these changes take place first in the longest and thickest hairs, that is, those of the head, and particularly those found on the top of the head. The hairs of the extremities change the last.

The hairs which have fallen off are rarely replaced, and those which have lost their color seldom resume it ; some examples of this phenomenon, however, have been seen.

The part which forms first is the sac which surrounds the bulb, a complete ovum, which, either in the primitive hairs or in those afterwards develôped, is already perfectly formed before the bulb, and is pierced by the hair which lengthens outwardly, as the capsule of the tooth is by the tooth, or the membranes of the ovum by the fetus. Probably its decay causes the death of the hairs ; for in old men whose hairs have fallen, we find no traces of tlrese sacs under the skin, while, when we see them as in the natural state, after those diseases where the hair has fallen off, a new growth arises from them.

§ 415. We may mention as sexual differences, that in the female the hairs are finer ; those of the head are longer, but those in other parts of the body are shorter. They are not entirely deficient in any of those parts where they exist in the male ; and in those places where they are largely developed in the male, they are also rather longer and more numerous in the female, especially when the functions and the differences dependent upon sex are not perfectly developed.

§ 416. Besides these differences arising from age and sex, the hairs present others also. In fact they vary according to the individuals, and in this relation they present, in the different human races, peculiarities, some of which are accidental, while others are very constairt :

1st. The color of the hair differs surprisingly in different individuals of the same race and of the same family. It varies from a very bright yellowish (white) to the deepest black, between which two extremes we find every imaginable shade of auburn, red, and brown. Other colors, as green for instance, cannot be considered as primitive : they depend on external influences, such as copper.

2d. As much may be said in regard to the thickness, number, and length of the hairs. Generally we may admit that the blackest are the thickest, and that the lighter are finer. Withof found in one fourth of a square inch of skin oire hundred and forty-seven black hairs, one hundred and sixty-two chestnut, and one hundred and eighty-two light hairs. This rule, however, is subject to exceptions, and the more as the hairs are not at equal distances in all individuals.

3d. The direction of the hairs is various. Usually they are even and straight ; often, however, they are more or less curled or frizzled.

The differences met with in the same nation may be considered as the differences of races. The most important ones have already been

OF THE EXTERNAL CUTANEOUS SYSTEM IN THE ABNORMAL STATE, 323

mentioned (§ 33) ; we shall only remark that these occur in all races : thus, there are negroes who have straight, long hair.

B. OF THE EXTERNAL CUTANEOUS SY-STEM IN THE ABNORMAL STATE.

417. The external cutaneous system possesses in a great degree the power of reproducmg itself. (1) AU its layers are reproduced, by whatsoever cause they may have been destroyed. But they do not reappear vdth characters perfectly sinülar to those which they have in the normal state.

The dermis is less elastic, and adheres more closely to the subjacent mucous tissue, than the natural dermis ; it is in fact blended wdth this tissue, and cannot be separated from it. Like aU other regenerated parts, it is less hard and has less spontaneous activity than the natural dermis. This explams the ease with which even old cicatrices are torn, and with which the new integuments of cutaneous ulcers are sometimes entirely destroyed.

The new dermis is at first exceedingly thin, delicate, and soft, more vascular, and of course redder, than the natural dermis ; it gradually becomes less vascular, whiter, firmer, and harder than the latter, and acquires almost all the qualities of a ligament. At the same time its aspect is smooth and shining, which depends undoubtedly on the absence of the papillae of touch and on that of the hairs, as well as on the tension of the new integument and its more intimate adhesion to the subjacent mucous tissue.

Its sensibihty is less than that of the primitive dermis, doubtless because of the absence of the nervous papillae. Perhaps also it receives fewer nerves than the latter.

These different phenomena are not however seen except when the dermis has been entirely destroyed ; for when the injury is only superficial, all marks of difference disappear with greater or less promptitude.

The new dermis is covered Yvith a rete mucosum and an epidermis ; but these latter are reproduced only gradually, as the fii'st formed layers always fall off.

The color of the rete mucosum is developed the last, and this is somethnes entirely deficient. Bichat pretends that its color is not reproduced when it has been removed, and that cicatrices are white in all people ; but this assertion is not perfectly correct, for in the negro the cicatrices of small pox are black,(2) and those which are developed after all injuries of the common integuments, are as black and sometimes blacker than the rest of the skin. (3)

(1) Moore, On the process of nature in the filling up of cavities, healing of wounds, and restoring parts which have been destroyed in the human body, London, 1782, sect. ii. p.,46.

(2) Meckel, in Mem. de Berlin, 1753, p. 81.

(3) Moore, lac. cit., p. 52. — Hunter, On the blood.

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GENERAL ANATOMY.

The nails and the hairs also possess the restorative power to a considerable extent.

The nails are reproduced not only in their natural places, but we have also seen them developed at the end of the second phalanx of the fingers when the third has been destroyed.

The hairs are not regenerated when the dermis has been destroyed entirely ; but they grow again more or less perfectly when they have fallen off from disease.

§ 418. The diseases of the skin extend to all the layers, or are confined to some only, which remark applies also to the anomalies of its form or to the alterations of texture.

§ 419. The prmcipal deviations of formation are,

1st. Its absence. The whole skin or some of its layers only may be deficient in one point or another. The first occurs when the cavities of the viscera are not entirely closed. But sometimes the epidermis is primitively deficient without any division or fissure of the body. The same is true of the nails and the hairs.

2d. Its excess, which is manifested, when the whole skin participates in it, by the existence of a greater or less number of rounded oblong excrescences in different parts of the body, almost always attended with a want of development in other parts.

As to the different parts of the cutaneous system, the most striking example of their excess is the extraordinary length of the hairs in places where they are usually very short. This deviation of formation is almost always attended with a greater development of fat and a darker tint of the skin.

The same deviations of formation may also be secondary or accidental.

The epidermis, the hair, and the nails, die after diseases of the skin, or in other morbid states consisting essentially m extreme weakness of the vital powers ; they are then detached from the body. The epidermis is constantly reproduced ; but this is not the case with the hairs and the nails. The albinism of the hairs also results from an imperfect nutrition, for it depends upon the slow or rapid death of their internal substance.(l)

The skin and its different parts can also acquire an increase of development. The dermis thickens, the papillæ of touch become longer. Warts arise from an unusual increase of some parts of the dermis, corns and callus from the thickening of the epidermis ; a considerable development and a horny hardening of the epidermis, forms also the essence of iclhyosis. There is much affinity between these different states and the excessive growth of the hairs of the head in plica polonica, which makes the transition from deviations of formation to alterations of texture.

§ 420. Alterations of texture are very frequent in the cutaneous tissue. Among the first we place a want of color in the rete mucosum,

(1) Weclcmeyer, HUior. pa/hol. pilorum, Göttingen, 1812.

Of THE EXTERNAL CUTANEOUS SYSTEM IN THE ABNORMAL STATE. 325

the leucethiopia, or leucosis, which is usually congenital, but which sometimes develops itself during life.(l)

Besides the inflammations, to which we give different names, according as they attack the different layers of the skin or the subjacent cellular tissue, the cutaneous system is subject to a great many affections which are pecuhar to it and known by the term exanthemata, the history of which belongs to pathology. Generally in the exanthematous diseases, the skin becomes like the mucous membranes, for its vessels receive more blood, it softens, furnishes liquid secretions, and the epidermis is almost always detached from it. As to the eruptions themselves, they are usually rounded, giving origin to a local increase of the peculiar life of the tissue which from a central point extends a greater or less distance, and assumes the characters of an inflammation which almost always results in the formation of a peculiar fluid. They may be considered as very imperfect organisms, or even as more or less successful attempts to produce ova, which they resemble in their round form, and from this circumstance, that they never become otherwise than fluid. Besides, the phenomena they present in their progress are in fact the same which are observed in entire organisms from their origin till their death. The chronic exanthemata are situated principally in the thickness of the dermis, while those which are acute in their progress appear at the external face of this membrane and in the vascular tissue.

§ 421. Abnormal formations of another species are developed, at least primitively, in the subcutaneous cellular tissue : such are fatty tumors, schirrus, cancer, and fungus hematodes, which extend sooner or later to the skin itself.

§ 422. Formations of the skin sometimes appear in abnormal places ; but this is less common in regard to the dermis than to the epidermoid portions, particularly the hairs. (2)

The most remarkable peculiarities presented by the accidental formation of the hair are,

1st. They are developed in the same circumstances as the regular hairs, that is, at the same time as the fat, and in the parts resembling the skin, either those newly formed, as the cysts, or those already existing, as the mucous membranes.

2d. They perfectly resemble the normal hairs, both in theh structure, their situation, and their changes. Like them they have roots, and almost always are implanted at first very firmly ; like them also they usually fall off after a certain lapse of time, and then appear mixed with fat. It is possible, however, that sometimes their roots are implanted in the fat 'only.

(1) G. T. L. Sachs, Historia naturalis duorum leucœthiopum auctoris ipsius et sororis ejus, Salzbach, 1812. — Mansfeldt, Réflexions sur la leucopathie considérée comme le résultat d'un retardement de développement, in the Journ. compl. des sc. méd., vol. XV. p. 250.

(1) Meckel, Mémoire sur les poils et les dents qui se développent accidentellement dans le corps, in the Journ. compl. du Diet, des sc. méd., vol. iv. pp. 122 and 217. — Bricheteau, Observation de kystes dermoïdes et pileux, suivie de quelques remarques sur ces productions organiques, in the Journ. compl. des sc. méd., vol. xv. p. 298.

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GENERAL ANATOMY.

3d. The places in which they occur most frequently are those where the activity of formation is the greatest, as in the ovaries. They are rarely seen in the testicles, although they have been found in these organs also.

The nails, or horny productions,(l) are developed more rarely in places differing from those which have been mentioned as their usual situations. The most general coirdilions of their formation are as follows : 1st, as far as our knowledge extends, they form only in the skin ; 2d, they develop themselves in cysts filled with fluid, which they pierce from within outward ; 3d, when destroyed, they are reproduced like the natural parts ; 4th, we generally find several at the same time in the same subject ; 5th, they are more common than in any other part in the loose portion of the skin, and especially in the integuments of the head, although they are sometimes found in places where this membrane is reflected on itself, for instance in the glans.

ARTICLE THIRD.

OF THE INTERNAL CUTANEOUS SYSTEM.

A. OF THE INTERNAL CUTANEOUS SYSTEM IN THE NORMAL STATE.

§ 423. We have already mentioned the division of the internal cutaneous system, or the system of the mucous membranes (§ 375). From the description we have given of it, it follows that this system represents a large canal extending from the mouth to the anus, presenting in its passage several prolongations and several simple or complex culs-de-sac, which comihunicate directly with the external cutaneous system. We observe besides, in all portions of the system of the mucous membranes, enlargements and contractions, which depend on the figure of the parts which it contributes to form, and the internal face of which it always lines.

The internal is much narrower than the external cutaneous system, but it is much longer and more distributed in the body.

§ 424. The external face of the mucous membranes is attached to the neighboring organs, which are almost always muscles — seldom, as in the gums, to bones — and sometimes to cartilages and fibrous tissue, as in the trachea — by a dense and solid layer of cellular tissue, ih which are the large vascular trunks which go to these membranes. This layer of cellular tissue is called the nervous coat ; and, according to Bichat, the form of the organ depends on its inner layer of mucous membrane.

(1) Caldani, in the Mem. della societa italiana, vol. xvi. p. 126. — Meckel, Sur les comes accidentelles, et en 'particulier sur celles qui viennent a,u gland, chez l'homme, in the Journ. corn, pl. des sc. mêd., vol iv. p. 91. — Bertrand, Note sur une production cornée, in the Archives gén. de méd., vol. v. p. 534.

OF THE INTERNAL CUTANEOUS SYSTEM IN THE NORMAL STATE. 827

This assertion, however, is not well founded ; for the' form of these organs is determined principally by the muscular tunic ; this is proved particularly in those places where this latter tunic is very thick, as in the uterus, the mouth, the pharynx, the esophagus, and the rectum.

In fact Bichat brings forward an cxperihnent which he believes proves his assertion. If we deprive a portion of intestine of its peritoneal, muscular, and nervous coats, and afterwards inflate the canal, the mucous membrane porjects at the place from which these coats have been removed. If a fold of the intestine be turned, and the mucous membrane and the nervous coat be removed, and it be inflated, the muscular and the peritoneal tunics also pass from the opening. But this experiment has always afforded me different results, which settle beyond a doubt that the form of the organ does not depend on its muscular coat.

In the former case, in fact, when the intestine remains in its proper place, the protrusion occurs when the muscular coat is removed, although it becomes more considerable after the separation of the nervous tunic. If, on the çontrary, the intestine be turned, the removal of the nervous and mucous coats is not followed by the protrusion of the muscular membrane, although when the latter is raised, the peritoneal coat rises slightly.

The union between the mucous membrane and the surrounding parts is not every where equally intimate. Usually, as in the whole intestinal canal, the nasal fossæ, the bladder, and the vasa defer entia, the adhesion is feebler than in some other parts, as of the tongue, the alveolar processes, and the uterus, where it is so intimate that the respective hmits of the parts can scarcely be distinguished.

§ 425. The internal and loose face of the mucous membranes is not perfectly smooth, like that of the external cutaneous system. It presents inequalities which in some parts are more distinct even than in the latter. Sometimes these inequalities depend on the great development of the nervous papillae, as in the tongue and the small intestines ; so that they are produced by these papillae and by the epidermis, that is in fact by all the layers of the mucous membrane, but also by it alone. Sometimes they give origin to folds, valves {'plicÅ“ s. valvulÅ“), formed either by the nervous coat and the mucous coat alone, or at the same time by the muscular coat. The former is much more common than the latter. Among these folds are arranged the valves of Kerkring in the intestinal canal, the folds of the internal face of the gall-bladder, of the vesiculæ séminales, and of the neck of the uterus, the wrinkles of the stomach and of the vagina. Among the folds of the second kind may be cited the pyloric and ileo-cæcal valves. These latter are found in that part where the function of the organ to which they belong requires a barrier or a line of demarkation between its different sections. The differences of the first kind are either constant or not. Thus, the folds of the intestines are always found, while those of the stomach and of the vagina are inconstant. The first, like those dependent on the development of the nervous papillae, arise from the

328

GENERAL ANATOMY.

extent of surface presented by the development of the mucous membrane ; while, on the contrary, those of the stomach appear because the mueous membrane is less contractile than the surrounding muscular tunic. The wrinkles in the vagina are inconstant for the same reason as the folds of the stomach ; for as they are more or less completely effaced by repeated distensions of this canal, this peculiarity demonstrates that their existence and their absence depend on the same cause.

§ 426. The internal differs but slightly from the external cutaneous system in its texture; but, in this respect, it varies more than the external in different parts of the body, doubtless because of the greater variety of functions it executes, according to the nature of the organs the internal face of which it lines.

The chief differences are,

1st. The manner in which the mucous membrane is bounded externally, or in which it is continuous with the surrounding parts. We have already examined this question (§ 424).

2d. The relations of the layers to each other. The mucous membranes differ from the external cutaneous system, as we cannot, in all parts, insulate the layers which constitute them.

In fact, these layers are so intimately united in almost every part of the internal cutaneous system, that ordinary means have in vain been employed to demonstrate them. Of this we have proofs in the mucous of membranes of the urinary apparatus, of the genital organs, and of most the intestinal canal, where blisters during life, and maceration after death, will not prove the existence of an epidermis, or more especially of several superimposed layers. On the contrary, the epidermis may be insulated in the mouth and the esophagus ; it is also more or less perceptible on the surface of the glans, in the meatus auditorius, in short, as before stated (§ 384), in most of those places where the internal cutaneous system is continuous with the external. It is however softer, more brittle, and detached with greater difficulty in a certain extent, than that of the skin, although in several parts, for instance in the tongue, its thickness exceeds that of the epidermis which covers most of the external regions of the body.

It is very doubtful if the epidermis exists in those places where we cannot by any means insulate it ; and although Haller, Bichat, and other physiologists, think its existence is proved by the appearance of membranes having the form of the canals from which they are expelled ; still the form of these membranes may be well explained in several other ways. In fact,

a. It is possible that these may be new formations produced by the inflammation of the mucous membranes ; which is more probable because they appear when the organs are inflamed, and abnormal membranous expansions are not only developed very often on the surface of inflamed serous membranes, but also an expansion of this kind, the caducal membrane, is normally produced, in the uterus, either by coitus followed by impregnation or by a morbid state without coitus.

OF THE INTERNAL CUTANEOUS SYSTEM IN THE NORMAL STATE. 329

b. The expelled membrane also may be itself a mucous membrane separated from its connections by gangrene, since we see the skin and other organs detached in their whole thickness from the same cause.

The existence of the epidermis as a distinct layer is not proved by the thickening, the hardening, and the dryness which the mucous membranes experience when they have been often irritated, or exposed for a time to the action of the external air. Finally, it is not demonstrated by the facility with which the mucous membranes support these unusual relations with external objects ; for all we can conclude from this is, that the mucous membranes have on their free surfaces a tissue analogous to the epidermis.

We discover also fewer traces of a distinct rete mucosum, at least unless we consider as such a whitish fluid found between the epidermis of the tongue and its papillæ.

The dermis of the mucous membranes offers as many differences ; and as they are formed in most of their extent of only a single layer, we must refer almost exclusively to this layer the principal variations they present, and which still remain for us to examine.

3d. The thickness. It varies much. The dermis of the urinary organs, of the respiratory organs, and of the genital organs, is uspally very thin ; that of the intestinal canal and of the stomach is thicker ; that of the esophagus still thicker, but always less so than that of several parts of the mouth, as the palate and the gums. The dermis of the mucous membrane of the nose has also considerable thickness.

4th. The development of the capillary .tissue. We may justly compare, as Bichat has done, the villosities {villi) of the mucous membranes to the papillæ of touch (§ 394). Like the latter, they are composed of cellular tissue, in the substance and on the surface of which blood-vessels and lymphatics are certainly distributed, and which probably receives nerves also, although we are not certain that the latter exist every where. The vessels are demonstrated by injections : this cannot be doubted when the injected parts are examined with a microscope. The nerves are seen distinctly in some parts, as in the tongue ; but farther, for instance in the intestinal canal, microscopical observations made with the most scrupulous care demonstrate only a simple granular structure in the villosities. We have not been able to observe openings in them with certainty.

The size and development of the papillæ of the mucous membranes are not everywhere the same. In several parts, as in the tongue and the small intestine, these papillæ are more developed than elsewhere, and are visible without any preparation, for instance without raising the epidermis, as is necessary in the skin. In the lips and penis they are considerable, but in those parts the epidermis covers them. Every where else they are extremely small and even imperceptible.

We particularly remark that the degree of their development is in direct relation with the wants and functions of the organs, for their volume increases in all those parts where a great increase of surface is necessary.

VOL.I

42

830

OEKEnAL ANATOMY.

6 th. The glands of the mucous membranes are much more developed than those of the common integuments. They always represent culsde-sac, and are more distinct in some parts, as around the mouth, than in others, especially in most of the extent of the mucous membranes, where they exist as simple depressions. Their special properties will be mentioned when treating of the glands. We shall only observe in this place that their number and volume are inversely as those of the villosities ; of this we may be convinced by comparing the membrane of the palate and tongue with that of the small and large intestines.

6 th. The continual moisture on the internal and free surface of the mucous membranes depends on the mucous glands, on the peculiar activity of the vessels of the mucous membranes, and on their slight exposure to the drying action of the air. The fluid secreted by these glands and called mucus, varies in .the different parts, although its essential properties are everywhere the same:(l) it is insoluble in water but absorbs much of it ; it coagulates neither by heat nor cold, and when dried becomes transparent.

7th. The color of the mucous membranes is not every where the same ; usually they are light red.

8th. These membranes are considerably softer than the external skin.

9th. They are also more vascular.

But they resemble more or less the common integuments in all these relations when placed in the same circumstances, especially in the inversion and the prolapsus of parts which they cover.

§ 427. Have the mucous membranes appendages similar to the nails and the hairs of the external cutaneous system ? We discover in them parts perfectly corresponding to these appendages, only in the abnormal state, and even then only hairs (§ 422) ; but we may consider the teeth as organs having many relations with them. Bonn(2) pointed out this resemblance, which has since been better developed by Walther(3) and by Lavagna,(4) and many facts might be adduced in its support ; but we shall consider this important question in descriptive anatomy when treating of the teeth.

(1) Fourcroy and Vauquelin, in Annales du Museum, vol. xii. p. 61, 67. — Berzelius, On the mucus of mucous membranes, in. General Views of the properties of animal fluids, in the Med. chir. trans., vol. iii. p. 245-247.

(2) De contin. membr., § xvi., in Sandifort, loc. cit., p. 276. An ergo membranula

hÅ“c folliculum constitucns, cutis oris propago est, per foramenula limbi^äxoducta ? An testula, quae déin crusta vitrea vocalur continuatio ejus enidcrmidjSIÊ, piaturæ unguium quodammodo, sed magis induratÅ“? . ' '

<3) Physiologie, vol. i. p. 174, 175.

(4) Esperienze c rifiessioni sopra la carie de' denti umani coll' aggiunta di un nuoco saggio sulla riproduzzionc do' denti negli animati rosicanti, Genoa, 1812, p. 164-198.

OF THS ir^TERÃŽfAL CUTANEOUS SYSTEM IN THE ABNORMAL STATE. 331

B. OP TUE INTERNAL CUTANEOUS SYSTEM IN TUE ABNORMAL STATE.

§ 428. We are deficient in observations to enable us to decide, if the mucous membranes grow again after having been destroyed, or if, where they have appeared to be reproduced, there has been only a contraction and reunion of the sound parts. (1)

§ 429. The mucous membranes present many anomalies. Their deviations of formation, especially the primitive, coincide almost always with analogous states of the whole organ, the internal face of which they line : such are, fissures, prolongations in form of sacs, contractions, inversions, &c. In these different cases all the layers vary in the same maimer from the normal state.

In fact in other circumstances the upper layers also present simultaneous anomalies : but these are of a different nature. Thus when the mucous membranes are considerably distended by their passage as hernias through the muscular coat, and which are known, particularly in the intestinal canal and the bladder, by the term diverticulmn spurium, the fibres of the muscular tunic are separated from each other.

We however observe abnormal processes which belong only to tho mucous membranes, independently of the other layers.

§ 430. These last anomalies form the transition from deviations of formation to changes of texture, since they are sometimes simple prolongations, such as the valves in the intestinal canal, but much more frequently excrescences, new formations, the texture of which differs more or less from that of the normal mucous membranes. We may remark, generally, that they are seen rather more frequently at the ex- ‘ tremities of the internal cutaneous system, near its union with the external, in the nasal fossæ, the buccal cavity, the pharynx, the rectum, the uterus, and the vagina. They are not however more common, the nearer they are to the limits of the external cutaneous system ; they are, on the contrary, almost always a little distant from these limits, so that for instance the ' excrescences of the nasal fossae are developed more frequently in the maxillary sinus, those of the buccal cavity in the back part of the mouth, those of the urinary apparatus in the bladder, those of the female genital system in the uterus or in the vagina, and we are mrable to tell to what this peculiarity must be ascribed.

The excrescences'spoken of are termed polypi. They are attached to the internal face of the mucous membranes by a long or short, broad oi narrow peduncle, and are loose in their cavities. Their structure is not always the same. They are generally formed of a very homogeneous substance ; sometimes however we see fibres perpendicular to the substance which supports them. They vary also in consistence, being sometimes hard, sometimes soft and mucous. They sometimes receive a great many very irregular vessels which form

(1) Thomson, Lectures on inßammatwn, Edinburgh, 1813, p. 421, 422.

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GENERAL ANATOMY.

large elnuses ami have no proper pariet.es, but in others, vessels cannot be distinguished. Sometimes they are very inconvenient from their size and from the compression which they exercise. Sometimes they injure the health by frequent hemorrhages from their surfaces or from their ruptured vessels. Sonretimes they inflame and suppurate. The place where they are developed usually shows a great tendency to reproduce them when they have been extirpated.

Schirms and cancer are also peculiar to the mucous membranes and to the glandular system ; they may be considered as resulting from the development of these membranes. These abnormal productions appear in some parts more frequently than in others, and are generally seen in those where polypi are developed. The parts, however, most frequently affected, are the female genital organs and the rectum ; they also are often developed in some other points, more particularly where polypi rarely grow, as in the pyloric orifice of the stomach.

This disease is unquestionably situated in the mucous crypts, and arises from the frequent irritation of the parts in which it is developed. It often contracts the cavity of the organ, because of the considerable thickening usually resulting from it.

It is rare that the mucous membranes ossify, or that osseous matter is deposited on their posterior face ; but round, fatty tumors are often developed in several places, among others in the esophagus and the small intestine: Monro(l) and Vicq d'Azyr(2) have denied the existence of these bodies, but wrongly ; although other tumors, entirely different in character, may possibly have been confolmded with them.

The general condition of all these anomalies is the increase of the formative power, inflammation, which however often attacks the mucous membranes without giving place to them.(3) One of the most

(1) Encylc. mêth. anat. pathoL, p. 343.

(2) Morbid anat. of the human gullet, Edinburgh, 1815, p. 196.

(3) As the mucous membranes were not considered in a general manner before the time of Pinel and Bichat, we seek in vain in the writings of previous authors for general views of diseases of this system ; but if we reflect that, properly speaking, they form the lungs, the stomach, the intestines, and the appendages of these viscera, we have only to study what has been written on the morbid affections of the latter to have a knowledge of their diseases. The works of Bonnet and of Morgagni contain many valuable facts upon the pathological anatomy of the mucous membranes. Pinel arranges among the inflammations of these membranes all the catarrhal affections of the ancients; or rather he has admitted as inflammations of these organs only the catarrhs (flux sereux, muqueux, &c.) of his predecessors. No one however had treated particularly of the subject when P. A. Prost published his Médecine éclairée par l'observation et l'ouverture des corps, (Paris, 1804, 2 vol. in 8vo.) He there establishes from a great many facts the following propositions : irritation of the mucous membrane of the intestines extends to the animal centre without pain : the excitement, the agitation, the derangement of its functions are relative to the susceptibility of these organs, to the causes which irritate them, to the natural disposition, and to the sensibility of the individual. The alterations of these viscera have more influence on the brain in proportion as their arteries are more developed, the red blood more abundant in their extent, and the means of irritation more active. The pains of the abdomen depend on the state of inflammation of the peritoneum and of the surrounding cellular tissue. Inflammation of the mucous membrane of the intestines, when very active, frequently extends to the peritoneal coat, but the latter naay be inflamed, although the mucous coat is healthy. The prostration of the ani

OP THE INTERNAL CUTANEOUS SYSTEM IN THE ABNORMAL STATE. 833

usual consequents of this inflammation, especially when it has continued a long time, is the thickening of this membrane. Ulcers are not unfrequently developed there ; but the mucous membranes can suppurate without ulceration, doubtless on account of the great analogy which exists between their natural secretion and pus. The unattached surface of the inflamed mucous membranes often secretes a greater or less quantity of coagulable substance which gives rise to solid or hollow cylinders. This is seen for instance in croup, {angina membranacea s. jjolyposa.) The parietes of the mucous membranes very seldom adhere after exsudations of this matter, but they often unite after ulcers, especially in those places where union is not impeded by motion and the continual passage of foreign substances.

mal centre results from the absence of red blood from the intestinal mucous surface, whether there be alteration and thickening-, hardness, fungosity, infiltration, ulceration of this membrane, or even if these affections do not exist. Finally, alterations of the intestines with or without inflammation, are in relation with the last symptoms of the animal functions preceding death. Prost could not but deduce from these general facts a medical theory very different from that taught before his time ; but he did not draw from his observations definite conclusions : confined as he was by the despotism of classifications, he made only an indecisive application of them to pathology.

Broussais has gone still farther. After censuring the exaggerations of Prost he concludes by attributing all essential fevers to the inflammation of the mucous membranes, especially those of the stomach. Inflammatory, gastric, bilious, mucous, adynamic, ataxic, and typhoid symptoms result, in his opinion, directly or sympathetically, from this inflammation : no inflammation of any organ whatever can give rise to the symptoms of simple acceleration of the circulation, unless the mucous membranes of the stomach are more or less affected. He ascribes to the acute, chronic, latent, obscure inflammation of these membranes, a host of diseases, as the exanthemata, gout, rheumatism, vesanies. The danger of most acute or chronic diseases arises principally from the inflammation of the mucous membranes which the physician should foresee, prevent, and combat ; finally it is the most frequent and gravest disease, that which affects the rest of the organization in the greatest degree, and a profound knowledge of which is the key to pathology. Broussais has also given a fine history of the inflammation of the pulmonary and gastro-intestinal mucous membranes, and important ideas upon the inflammation of the other mucous membranes. He thinks that all the alterations of texture of which they are susceptible depend on acute or chronic inflammation. However exaggerated these ideas of inflammation of the membranes may be, it is no less true that they are erroneous only in being too general, and that Broussais has supplied a great deficiency in pathology, in pathological anatomy. His opinions and their varieties may be found in the Histoire des phlegmasies, ou inflammations chroniques, Paris, 1808, 2 vol. in 8vo. ; id. 1816, 2 vol. in 8vo. ; id. 1821, 3 vol. in 8vo., in his Examen des doctrines médicales généralement adoptees, Paris, 1821, 2 vol. in 8vo., and in his Annales de la médecine physiologique, Paris, 1822. Boisseau endeavored in 1817 to prove that gastritis did not constitute all essential fevers, and that inflammations of the mucous system were not the only ones which produced fevers. See his Réflexions sur la nouvelle doclrin£ médicale, in the Journal universel des sciences médicales, vol. vii. p. 1, and vol. viii. p. 257 ; his article, Eièvre in the Dictionnaire abrégé des scie?ices médicales; his Pyrétologie physiologique, Paris, 1823, in 8vo. ; id. 1824, in 8vo. — See also Roche, Réfutation des objections faites à la nouvelle doctrine desflevros, Paris, 1822, in 8vo. — Bégin, Physiologie pathologique, Paris, 1821, in 8vo. — J. Cloquet Mémoires sur les ulcérations des intestins, in Nouveau journal de médecine, vol. i. p. 107. — Scoutetten, (De V anatomie pathologique en général, et de celle de V appareil digestif en particulier, Paris, 1822, in 4to.), and Andral, (Alédecine clinique, Paris, 1823, in 8vo.), have carefully described marks of inflammation of the mucous tissue. — Goupil, Exposition des principes de la nouvelle doctrine médicale, avec un PréeU de thèses soutenues sur ses différentes parties, Paris, 1824, in8vo. F. T.

834

GENEUAI. ANATOMY.

§ 431. Do tho mucous membranes assist, in forming the exanthemata so common in the external cutaneous system, and which appear under such various forms ?(1)

Perliaps upon no question in pathology are there so many different opmions.

Exanthematous diseases doubtless form in the external portion of the mucous membranes near the places where they are continuous with the external cutaneous system when the latter is itself affected. Besides, these membranes frequently inflame with eruptive diseases of the skin. But do the exanthemata assume there the same form as in the common integuments ? The great difference in the texture of the two parts authorizes us to think, that the cutaneous exanthema differs much from that of the mucous membranes, and experience teaches, that in many exanthematous diseases, for instance in small pox, all the mucous membranes are often acutely inflamed, but no pustules are found in them, although they cover the skin. Some observations however, as those of Wrisberg(2) and Blane,(3) estehlish incontestably, contrary to the opinions of the most celebrated physicians, that, when the variolous pustules exist in the skin, they sometimes form also in the mucous membranes, especially those of the air-passages and alimentary canal, and differ but little from those on the surface of the common integuments.

§ 432. The mucous membranes are not unfrequently developed abnormally ; usually, however, after inflammation when it has terminated by suppuration. We think that every suppurating surface may be compared to an imperfect mucous membrane.

After inflammation, the cellular tissue, imbibing the coagulable part of the blood whicli has infiltrated into its texture, changes into a soft and whitish ihembrane, which soon acquires the power of secreting a peculiar fluid, called pus ; so analogous to mucus that we cannot distinguish them by our reagents. This membrane is intimately united to the subjacent cellular tissue and soon receives numerous vessels. Its surface, which is at first smooth becomes uneven, and numerous small tubercles, formed of vessels and cellular tissue, arise ; these are called granulations ; in this state pus is continually secreted, until the number of its vessels diminishes, the granulations waste, and in their place is developed a substance which resembles more or less the natural membrane which previously existed. The mucous membranes then suppurate more readily than all other parts ; and what is more remarkable, they have the power of forming pus, although there is no previous destruction of their tissue and the formation of a new one — indispensable conditions in other organs. The same perhaps is true of the serous membranes : but they then resemble the mucous membranes very much, as is shown by their thickening, softening, the increased number of vessels in their substance, and their consequent redness.

(1) Scoutetten, loc. cit. — Aiidral, loc. cit.

(2) Sylloge comment., p. 62.

(3) 'trans.foT impr. of mcd. and surg. knowl., vol. iii., London, 1812, no. 31, p. 426, W.

0F THE GLANDULAR SYSTEM IN THE NORMAL STATE. 835

The accidental cysts are often similar to the mucous membranes, both in regard to their structure and the nature of the fluid which they contain ; and Bichat has gone too far in referring them all to the class of serous membranes. We have found more than once, in the ovaries and in the uterus, large and small cysts which resemble the mucous much more than the serous membranes. We beheve also there is an exact relation between their structure and the nature of the fluid contained by them, for we have recognized that the cysts filled with serum resemble much the serous membranes, while others filled with thicker mucilaginous or purulent matter are more similar to the mucous membranes.

The purulent cysts, which are connected with the surrounding cellular tissue less intimately than are ordinary abscesses, naturally lead to the latter.