STRUCTURE OF THE COBIUM. cciii 



from their recesses when the cuticle is detached, appearing then like threads 

 proceeding from its under surface. 



Chemical composition. The cuticle consists principally of a substance peculiar 

 to the epithelial and horny tissues, and named keratin. This horny matter is in- 

 soluble in water at ordinary temperatures, and insoluble in alcohol. It is soluble in 

 the caustic alkalies. In composition, it is analogous to the albuminoid principles, 

 but with a somewhat larger proportion of oxgyen ; like these, it contains sulphur. 

 Besides keratin, the epidermis yields, on analysis, a small amount of fat, with salts, 

 and traces of the oxides of iron and manganese. The tissue of the cuticle readily im- 

 bibes water, by which it is rendered soft, thick, and opaque, but it speedily dries 

 again, and recovers its usual characters. 



The true skin, cutis vera, derma, or corium, is a sentient and vascular 

 texture. It is covered and defended, as already explained, by the insen- 

 sible and non-vascular cuticle, and is attached to the parts beneath by a 

 layer of areolar tissue, named "subcutaneous," which, excepting in a few 

 parts, contains fat, and has therefore been called also the " panniculus adi- 

 posus " (rig. cxxin. d.). The connection is in many parts loose and movable, 

 in others close and firm, as on the palmar surface of the hand and the sole of 

 the foot, where the skin is fixed to the subjacent fascia by numerous stout 

 fibrous bauds, the space between being filled with a firm padding of fat. In 

 some regions of the body the skin is moved by striated muscular fibres, 

 which may be unconnected to fixed parts, as in the case of the orbicular 

 muscle of the mouth, or may be attached beneath to bones or fasciae, like 

 the other cutaneous muscles of the face and neck, and the short palmar 

 muscle of the hand. 



Structure. The corium consists of a fibro-vascular layer, which is sup- 

 posed to be bounded at the surface next the cuticle, by a fine homogeneous 

 basement-membrane or membrana propria, like the corresponding part of 

 the mucous membrane. No such superficial film can, it is true, be raised 

 from the corium, but, from its distinct presence in small gland-ducts which 

 are continuous with the corium, and from the fact that a thin homogeneous 

 membrane lies between the commencing cutis and cuticle in the embryo, it 

 is presumed that a limitary membrane of this sort ought to be reckoned as 

 an element of the corium, although, as in the analogous case of the mucous 

 membrane, it cannot be shown to exist generally over the surface. The 

 Jibro-vascular part is made up of an exceedingly strong and tough framework 

 of interlaced fibres, with blood-vessels and lymphatics. The fibres are chiefly 

 of the white variety, such as constitute the chief part of the fibrous and areolar 

 tissues, and are arranged in stout interlacing bundles, except at and near 

 the surface, where the texture of the corium becomes very fine. With these 

 are mixed yellow or elastic fibres, which vary in amount in different parts, 

 but in all cases are present in smaller proportion than the former kind ; also 

 connective tissue corpuscles, fusiform or ramified, and for the most part reticu- 

 larly anastomosing. The interlacement becomes much closer and finer 

 towards the free surface of the corium, and there the fibres can be discovered 

 only by teasing out the tissue, which often acquires an almost homogeneous 

 aspect. Towards the attached surface, on the other hand, the texture be- 

 comes much more open, with larger and larger meshes, in which lumps 

 of fat and the small sudatory glands are lodged ; and thus the fibrous part 

 of the skin, becoming more and more lax and more mixed with fat, blends 

 gradually with the subcutaneous areolar tissue to which it is allied in elemen- 

 tary constitution. Bundles of plain muscular tissue are distributed in the 



