CHAPTER XXXV.
APPENDAGES OF THE SKIN.
717. The HAIRS are appendages of the skin, and, like the cuticle, they are a product of secretion. They have no blood-vessels or nerves, and, consequently, no vitality. The hairs take their origin from the cellular membrane, in the form of bulbs. Each hair is enclosed beneath the surface by a vascular secretory follicle, which regulates its form during growth. In texture, it is dense, and homogeneous toward the circumference, and porous and cellular in the centre, like the pith of a plant. Every hair has on its surface pointed barbs, arranged in a spiral manner, and directed toward the root of the hair; so that, if a hair be rolled between the fingers, it moves only in one direction.
Fig. 118.
Fig. 118. The hair follicle (1) is represented as imbedded in the cellular membrane, (2,) which is situated beneath the skin. 3, 3, The membranous sac, which has a narrow neck, opening externally by a contracted orifice, through which the hair (4) passes. Its internal surface is smooth, and not adherent to the hair, but separated from it by a reddish fluid. From the bottom of the sac (5) the pulp of the hair arises, and passes through the skin at 6.
717–723. Describe the appendages of the skin. 717. Why have not hairs vitality? Where do they take their origin? Give their structure. What is represented by fig. 118?