thickness in general proportioned to the size of their body, destined
to defend the subjacent parts, to carry out a considerable portion of
the residue of nutrition and digestion, and to place it in relation
with external bodies. It is in man a sensitive boundary, placed at the
extremity of the domain of his mind, where these bodies continually
touch, for the purpose of establishing the relations of his animal
life, and of thus connecting his existence with that of every thing
which surrounds him. This covering is the _dermis_ or skin. We shall
call the whole of it the Dermoid System.
ARTICLE FIRST.
FORMS OF THE DERMOID SYSTEM.
The covering which forms this system, being proportioned to the parts
that it covers, is applied to these parts, adapted to their great
inequalities, and allows the largest external prominences to be
visible, but conceals a great number on account of their small size;
thus the appearance of the body stripped of skin differs very much from
that with the skin on.
This covering everywhere continuous is reflected through different
openings in the interior of the body and goes to give origin to the
mucous system. The limits between the two systems are always marked by
a reddish line; within this line is the mucous system, without it the
dermoid. Yet the demarcation is not as striking in the organization
as in the colour. Both are confounded in an insensible manner. In the
neighbourhood of these openings, of those of the face especially, the
dermoid becomes more delicate. At the commencement of these openings,
the mucous borrows more or less, as I have said, the characters of the
first.
I. _External Surface of the Dermoid System._
This surface, everywhere contiguous to the epidermis, is remarkable
for the hairs which cover it, for the oily fluid which constantly
lubricates it, for the sweat that is deposited on it, for the sense of
feeling of which it is the seat and which the internal surface does not
possess. We shall in this article consider only the external dermoid
forms, without regard to these different objects.
We see upon this surface different kinds of folds.
1st. Some are owing to the subjacent muscles which, being intimately
connected with the dermis, forming almost a part of it, wrinkle it
when they contract. Such are the wrinkles on the forehead; those in
the form of rays which the orbicularis produces around the eye-lids,
&c.; those of which the cheeks are the seat, when the great and small
zygomatic, &c. contract; those which the orbicularis of the lips
produces around the mouth, when it contracts it by diminishing its
opening, &c. All these folds are owing to this, that on the one hand
the skin cannot contract like the muscles, and that on the other it
is necessary that it should occupy less space in length at the instant
these are shortened. They are of the same nature as those of which
the mucous surfaces, that of the stomach in particular, become the
seat in the contraction of the fleshy layer which is contiguous to
them. Thus the direction of these folds is always perpendicular to
that of the subjacent muscles whose fibres they cut at a right angle.
We are accustomed to attach much importance to the existence of these
wrinkles in the expression of the passions; no doubt because then they
are strongly marked. In fact the breadth of the face of man makes it
well adapted to their development, whilst that of animals is badly
formed to produce them. Thus their eye, rather than the features of the
face, is the moveable picture which is differently sketched at every
instant by the various feelings of anger, hatred, jealousy, &c. The
wrinkles of the human face contribute very much to the expression of
the countenance, they compose in part the physiognomy, and mark its
different shades.
The wrinkles of the scrotum are analogous to these; they depend upon
the contraction of the subjacent cellular texture, in which some fleshy
fibres appear also to exist.
2d. There are other wrinkles which are owing also to the motions, but
not to those of the subjacent muscles. There are those of the sole of
the foot, and especially those of the palm of the hand. There is not
there any sub-cutaneous muscle adhering to the skin, except the small
palmar muscle, which has no agency in these wrinkles that are formed at
the places where the skin is constantly folded in flexion. Thus there
are many of them about all the articulations of the phalanges. In the
palm of the hand, we see three principal ones, one at the base of the
thumb, produced by the motion of opposition, another at the anterior
part of the palm, occasioned by the flexion of the four last phalanges
which are bent towards the thumb, and the third is found in the middle
of the palm. The dermis is folded between these depressed lines, in
the motions in which the hand is hollowed. Many other small folds
corresponding with less evident and less frequent motions, cut these at
different angles.
On the back of the foot and hand, there are many wrinkles about each
articulation of the phalanges, when they are extended. They disappear
in flexion, and are owing to this, that nature, on account of the
motions, has made the skin more loose at this place, and broader in
proportion to the parts it covers. About most of the articulations,
there are analogous folds, but they are much less evident, because the
skin adheres less to the neighbouring parts. Upon the whole trunk, the
arm, the fore-arm, the thigh and the leg, we see no depressions but
those from the muscular prominences.
3d. There is a third species of wrinkles, or rather cutaneous
impressions, which are not very evident, found especially on the sole
of the foot and the palm of the hand and which we easily distinguish
from the preceding; they are those which indicate the rows of the
papillæ. The surface of the trunk presents hardly any thing similar.
4th. Finally, there are the wrinkles of old age, which are of a wholly
different nature. The sub-cutaneous fat having in part disappeared, the
skin becomes too large for the parts it covers; now as it has lost with
age its contractility of texture, it does not contract, but folds in
various directions. Thus where there was the most fat, as on the face,
these wrinkles are the most evident, they resemble those that appear on
the abdomen after several pregnancies, dropsy, &c. In young people, if
emaciation takes place suddenly, the skin contracts, and no wrinkle is
formed.
II. _Internal Surface of the Dermoid System._
This surface answers everywhere to the cellular texture which is loose
upon the trunk, the thighs, the arms, &c. and which is condensed
upon the cranium, the hand, &c. In most animals, a fleshy layer
called panniculus, and of a form analogous to that which is almost
everywhere subjacent to the mucous system of man, separates the skin
from the other parts, and communicates to it various motions. In man,
the dermoid system exhibits here and there traces of this internal
muscle, as is observed in the platysma myoides, the occipito-frontalis
and most of the muscles of the face. There is nothing similar on the
trunk, extremities, &c. Man is as much inferior in this respect to most
animals, as he is superior by the arrangement of his facial muscles.
Thus observe that whilst in him all the passions are painted as it
were upon the face, and the whole exterior of the trunk remains calm
in these tempests of the mind, this exterior is convulsively agitated
in animals. The mane of the lion becomes erect, the whole skin of the
horse moves, a thousand different agitations animate the exterior of
the trunk of animals, and make it a general picture on which is painted
all that passes in the interior. You can determine from behind, in
many animals, by seeing only their bodies, that they are agitated with
passion; cover the face of man, the curtain is drawn over the mirror of
his mind; thus almost all nations leave it uncovered. The physiognomy
is in this respect, if we may so say, more generally spread over the
exterior, in animals with a fleshy panniculus.
Besides the cellular texture, the dermis is almost everywhere
subjacent to the muscles in the trunk; but, foreign to the motions of
these muscles, it receives no sensible influence from them. In the
extremities it is found separated from the fleshy layers by aponeurotic
expansions. Many vessels wind under it; the great veins pass through
its texture; many arterial ramifications go upon its surface, and many
nerves between these ramifications.
ARTICLE SECOND.
ORGANIZATION OF THE DERMOID SYSTEM.
I. _Texture peculiar to this Organization._
This texture comprehends, 1st, the chorion; 2d, that which is called
the reticular body; 3d, the papillæ. The chorion is the essential part
of the dermis; it is that which determines its thickness and form. The
reticular body appears to be but little distinct from it. The papillæ
arise from it also, but are more evident.
_Chorion._
The chorion is of a very variable thickness. 1st. In the head, that
of the cranium and that of the face exhibit an opposite arrangement.
The first is very thick and also dense and compact, which is owing
especially to the numerous hairs that go through it. The second,
everywhere fine and delicate, is particularly so upon the eyelids and
the lips. 2d. The chorion of the trunk is posteriorly and all along the
back, of a thickness almost double that of its anterior part, where it
is nearly the same upon the neck, the chest and the abdomen. I would
except however that of the penis, the scrotum, the great labia and the
mammæ, in which its delicacy is greater than any where else. 3d. In the
superior extremities it is nearly uniform upon the shoulders, the arm
and the fore-arm; on the hand it increases a little in thickness and
more in the palm than on the back. 4th. This thickness is generally
much more evident on the thigh and the leg, where there are more
muscles, than on the arm or the fore-arm. On the foot, it increases as
on the hand, less in the dorsal than in the plantar region, which is
the thickest of all the parts of the dermoid system; which is owing
principally in the natural state to the arrangement of its epidermis.
We see from this, that though everywhere continuous, the chorion is
very different in its different parts. The relation of its thickness
with its functions is easily perceived on the hand, the foot, the
cranium, &c. Elsewhere we cannot so well see the reason of these
differences, which are notwithstanding as constant.
Woman has a chorion generally less thick than that of man; compared in
all the regions, it exhibits in the two sexes a sensible difference; on
the mammæ especially, it is much more delicate in woman. That of the
great labia however is proportionally thicker than that of the scrotum.
In order to understand perfectly the intimate structure of the chorion,
it is necessary to examine it at first on its internal surface, after
having carefully separated it from the fatty cellular texture, to which
this surface adheres more or less intimately. We see then that it is
differently arranged according to the regions.
1st. On the sole of the foot and the palm of the hand, we observe an
infinite number of white fibres, shining like aponeurotic fibres,
which are detached from this internal surface, form upon it a kind of
new layer, cross each other in all directions, leave between them,
especially towards the heel many spaces of different sizes, that are
filled with fat, separate more and more, and are finally lost in the
sub-cutaneous texture, nearly as the fibres of the brachial aponeurosis
insensibly disappear in the neighbouring cellular texture. Hence why
when we dissect the palmar and plantar integuments, we experience the
greatest difficulty in separating them entirely from the cellular
texture which is interlaced with these fibres; hence why also these
surfaces have not, on the parts which they cover, the mobility which
many others exhibit.
The density of the cellular texture contributes also something to this
arrangement which is essential to the functions of the foot and the
hand, which are designed to seize and grasp external bodies.
2d. The dermis of the superior and inferior extremities of the
back, of the neck, of the thorax, of the abdomen, of the face even
and consequently of almost all the body, is distinguished from the
preceding, because the fibres are much less distinct, and are not
lost in the cellular texture by being as it were confounded with it,
whence arises a remarkable laxity of the skin of these parts, and the
very great facility with which it is dissected; in a word because the
spaces between these fibres are much more narrow. These spaces appear
like an infinite number of holes irregularly placed at the side of each
other, containing most of them small fatty parcels of the neighbouring
texture, and exhibiting, when these small parcels have been carefully
removed, very evident vacuities. The fibres which form them, are
sufficiently near each other, to make you believe at first view, that
it is a surface pierced with an infinite number of holes, that has
been applied under the skin. On the contrary, on the hand and the
foot, towards the heel especially, it is a true net-work the spaces of
which are larger than the fibres that form them; this is the reverse
here. Be that as it may, these spaces in the internal surface of the
chorion are very favourable to the action of tannin which penetrates
the texture infinitely better from this side than from the opposite,
because it insinuates itself into these numerous openings. I have had
occasion to observe it in the human chorion which I have had tanned
for the purpose. Chaptal has observed that the epidermis is a real
obstacle to the action of tannin, and that on this account scraping
is a preliminary operation essential to tanning, since it allows the
skin to be penetrated on both sides; but even when thus scraped, it
receives the tannin much more easily on the side of the flesh than on
the opposite one.
3d. The chorion of the back of the hand and the foot, as well as
that of the forehead does not exhibit these numerous openings on its
internal surface; it is smooth and white, especially when it has been
macerated a little. It is precisely the same as that of the scrotum,
the prepuce and even the great labia. The texture of it is more
compact, no space is left in it, so that though more delicate than that
of the extremities and the trunk, it contains almost as much substance.
As to the chorion corresponding to the hair and the beard, we see in it
only the openings necessary for the passage of the hairs, and which are
wholly different from those of which I spoke just now, which form real
culs-de-sac, and do not pierce through the chorion.
Hence the internal face of the dermoid chorion exhibits three very
distinct modifications. The first and last are seen to a small extent,
whilst the second is almost general, with some differences however in
the trunk, the extremities and the head. Besides, these modifications
do not suppose a diversity of nature, but only of forms. Much separated
and arranged in fibres in the first, the dermoid texture is compact and
condensed a little in the second, and by this condensation renders the
spaces less distinct. But there is a means of seeing them everywhere
very well, where there is the least trace of them, and this is by
maceration. This means also shows the dermoid texture best. In fact,
when the skin has remained for some time in water, it softens, the
fibres of its chorion separate, and their interstices become more
distinct; then we see that the spaces exist not only on the internal
surface, but that they extend into its texture which appears to be
truly like a sieve in its whole thickness, so numerous are the spaces
arising from the interlacing of the fibres.
These spaces do not terminate in culs-de-sac towards the external
surface; they open upon this surface by many foramina which are very
evident in a skin that has been macerated for a month or two, and
which, in the ordinary state are almost imperceptible in some subjects,
and very visible in others. Besides, in order to see them it is
necessary to remove the epidermis; now as with the view of producing
this effect immediately we commonly employ the action of boiling
water or fire, the dermoid texture by this means acquires the horny
hardening, and they become much less apparent, whereas maceration not
only does not produce horny hardening of the skin, but it expands and
dilates it, which renders these foramina very evident. In some parts of
the skin and in certain subjects, we might then introduce the head of
a pin into them; in others they are less evident. These foramina never
pierce the dermis perpendicularly, all open obliquely to its surface;
so that a perpendicular pressure tends to close them and bring their
parietes in contact. I cannot compare their termination better than
to that of the ureters in the bladder; hence why the hairs which go
through them are never perpendicular, but oblique to the skin. We speak
incorrectly when we say that the hairs are planted obliquely; their
insertion in the bulb is perpendicular; it is in their passage through
the chorion that they change direction.
Besides, these foramina are not vessels, but mere communications
from the interior to the exterior through which pass the hairs, the
exhalants, the absorbents, the blood-vessels and the nerves which
go to the surface of the dermis; thus the subjacent spaces are only
cells in which are contained the vessels of the glands and of the
cellular texture. The dermoid texture should then be considered as a
real net-work, as a kind of cellular texture, the cells of which very
evident within, become less so on the exterior surface, with which all
communicate to transmit to it different organs. The chorion is then
the outline, the frame, if I may so say, of the cutaneous organ. It
serves to lodge in its spaces, all the other parts which enter into the
structure of this organ, and contributes to give them the form they are
to have, but is wholly foreign to them.
What is the nature of this texture, which enters especially into the
composition of the cutaneous chorion? I know not; but I think it has
much analogy with the texture of the fibrous system; the following
considerations support this analogy. 1st. On the heel, where the
dermoid texture has the fibrous form of the irregular ligaments, it
would be almost impossible to distinguish it from it, so uniform is
the external appearance; it has the same resistance and density; the
same sensation is experienced when it is cut with the bistoury. 2d.
The dermoid texture becomes yellow and transparent like the fibrous
by stewing. 3d. It melts gradually like it into gelatine. 4th. Like
it, except the tendons however, it strongly resists maceration. 5th.
Sometimes these two textures are identified; for example, the annular
ligaments of the wrist evidently send elongations to the neighbouring
dermoid texture. 6th. This texture can serve, like the fibrous, for the
insertion of muscles; we see it in the face, where many of the fibres
of the orbicularis of the lips and the eyelids, and almost all those of
the eyebrows, find real tendons in the fibres of the dermoid texture.
There is the same arrangement in the cutaneous palmar muscles.
All these considerations evidently establish many relations between the
dermoid and fibrous textures. Yet they are far from being the same. To
be convinced of this it is sufficient to observe how much their mode
of sensibility differs, and how different also are their diseases; it
seems at first as if there was no analogy between them in this double
relation. Yet the line of demarcation is by no means as great as it
appears to be. In fact the acute sensibility of the skin is not seated
precisely in this white texture, which is interwoven so as to leave
between its meshes the spaces of which we have spoken, and which we
see especially on the surface adhering to this organ. The experiment
mentioned in the article on the mucous system, and in which I irritated
the cutaneous organ from within outwards, evidently proves it. It is
the surface on which the papillæ are found that especially exhibits
this vital property.
On the other hand morbid anatomy proves that the internal surface
of the dermis, in which are especially found the texture and the
spaces of which we have spoken, is entirely free from most cutaneous
eruptions. This is no doubt true as it respects the small pox, the
itch and many species of herpes; I have satisfied myself of it as to
the vaccine vesicles, the miliary eruption, &c. &c. It is certain that
in erysipelas, the external surface only of the chorion is coloured
by the blood which enters the exhalants; thus the slightest pressure,
causing the blood to flow back, produces a sudden whiteness which soon
disappears by the return of the blood into the exhalants. It is this
which forms the essential difference between simple erysipelas and
phlegmon, in which not only the external face of the chorion, but its
whole texture and the subjacent cellular one are inflamed. In measles
and scarlatina, the redness is also very evidently superficial. These
phenomena accord with those of injections; for if they succeed at all
in children, the skin of the face and less frequently that of the other
parts, becomes almost entirely black. Now this blackness is much more
evident on the external than the internal surface of the skin, no doubt
because more exhalants are found in the first than in the second, which
the arterial trunks only traverse.
The preceding considerations evidently prove that the texture of the
internal surface of the chorion, and even that of its interior, have a
vital activity much less than that of the external surface; that this
texture is disconnected with all the great phenomena which take place
upon the skin, with those especially which relate to the sensations and
the circulation; that it is in the papillæ that the first are seated
and in the reticular body the second; and that it is almost passive
in nearly all the periods of activity of this double portion of the
dermis. Its functions, like those of the fibrous texture, suppose it
to be almost always in this passive state; they are only to defend the
body and to protect it from the action of external bodies. It is this
which forms our real covering; thus its properties are well adapted
to this use. Its resistance is extreme. It requires very considerable
weight to tear very narrow strips of chorion, when it is suspended from
them; drawn in various directions, these strips are broken also with
much difficulty.
Yet this resistance is much less than when tannin is combined with
the chorion. We know that when thus prepared, this portion of the
skin affords the strongest strings we have in the arts. I know but
two textures in the animal economy, which unite to such an extent
suppleness and resistance; these are this and the fibrous texture; and
this is a new character which approximates them. We have seen that
it requires a very considerable weight to break a tendon, a strip
of aponeurosis, or a ligament taken from a dead body. The muscular,
nervous, arterial, venous, cellular textures, &c. yield infinitely
more easily. If the dermoid texture had less extensibility, it might
advantageously supply the place of the tendons, the ligaments, &c. in
the structure of the body.
Since the chorion is foreign to almost all the sensitive and morbid
phenomena of the skin, let us inquire then in what part of the dermis
these phenomena are seated. These parts exist very evidently on the
external surface; now we find on this surface, 1st, what is called the
reticular body; 2d, the papillæ.
_Of the Reticular Body._