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.