THE SKIN AND ITS APl'KNDAGES 



397 



The arrector pili muscle (Fig. 278, c) is a narrow band, or bands, of 

 smooth muscle connected with the hair follicle. It arises from the 

 outer layer of the derma on the side toward which the hair slants, and 

 is inserted into the wall of the follicle at the junction of its middle 

 and lower thirds, the sebaceous gland being usually included between 

 the muscle and the hair (see below). The contraction of the muscle 

 thus tends to straighten the hair and to compress the gland. 



The sebaceous glands are with few exceptions connected with the 

 hair follicles. They are simple or branched alveolar glands. The 



Fig. 281. — Transverse Section through Root of Hair and Hair Follicle. (Kolliker.) 

 a, Hair; b, hair cuticle; c, cuticle of root sheath; d, Huxley's layer; e, Henle's layer;/, 

 outer root sheath; i, connective- tissue follicle. 



size of the gland bears no relation to the size of the hair, the largest 

 glands being frequently connected with the smallest hairs. The 

 glands are spherical or oval in shape and each gland is enclosed by a 

 connective-tissue capsule derived from the follicle or from the derma. 

 Beneath the capsule is a basement membrane continuous with the 

 vitreous membrane of the follicle. The wide excretory duct empties 

 into the upper third of the follicle and is lined with stratified squamous 

 epithelium continuous with the outer root sheath and stratum ger- 

 minativum. The lower end of the duct opens into several simple or 

 branched alveoli, at the mouths of which the epithelium becomes 



