The glands of the skin are of two kinds:

1, sebaceous or fat-forming; 2, sudoriparous or sweat glands.

Those from which the sebaceous secretion is produced are minute lobulated structures situated in the fibrous tissue of the derma (6, fig. 260). The sebaceous glands are provided with ducts, some of which open on the surface of the cuticle, but by far the greater number pour their secretion into the hair follicles. They are necessarily very numerous in animals which have a hair covering. These glands are always most abundant and of larger size and greater activity in those parts of the skin which are constantly subject to movement, as in the bends of joints, and it is extremely probable that at each flexion and extension of a joint a certain amount of sebaceous matter is squeezed out of the ducts, thus keeping the skin in a soft and supple condition. The sudoriparous or sweat glands are situated deeper in the substance of the true skin than those above described. Some of them even pass beyond it into the subcutaneous areolar tissue. These sweat glands are not lobulated as the sebiparous or sebaceous glands are, but consist of one or more long tubes twisted upon themselves so as to form a more or less rounded or ovoid gland, terminating in a single excretory duct (7", fig. 260). The canal by which the watery secretion is discharged on to the skin as "sweat" takes a somewhat spiral course, which becomes most evident as the tube passes through the epidermis to terminate in a minute opening on the surface.

Fig. 260. - Section of Skin, showing Glands and Hair Follicles.

1, Epidermis. 2, Derma. 3, Areolar Tissue. 4, Hair Follicle. 5, Hair. 6, Sebaceous Gland. 7, Sudoriparous or Sweat Gland. 7', Duct of Sweat Gland. 7", Opening of Sweat Gland.