112 



THE ESSENTIALS OF HISTOLOGY 



termed the lanugo. This is entirely shed within a few months of birth, 

 the new hairs being formed in downgrowths from the old hair -follicles 

 in the manner already mentioned. 



Hairs grow at the rate of half an inch per month. They are found 

 all over the body except on the palms of the hands and the soles of 

 the feet, and on the distal phalanges of the fingers and toes. They 



FIG. 136. 



A. Hair-rudiment from an embryo of six weeks a, horny, and 6. mucous or Malpighian 

 layer of cuticle ; ', basement-membrane ; m, cells, some of which are assuming an oblong 

 figure, which chiefly form the future hair. B. Hair-rudiment, with the young hair formed 

 but not yet risen through the cuticle. , horny, 6, Malpighian layer of epidermis ; c, outer, 

 d, inner, root-sheath ; e, hair-knob : /, stem, and g, point of the hair ; h, hair-papilla ; 

 , n, commencing sebaceous follicles. C. Hair-follicle with the hair just protruded. 



usually slant, and in the negro the hair-follicles are even considerably 

 curved. On the scalp they are set in groups, as is well seen in a hori- 

 zontal section. 



The hairs of animals are* often curiously marked by the arrange- 

 ment of their medulla, the markings being often characteristic of the 

 particular species. 



Muscles of the hairs. A bundle of plain muscular tissue is attached 

 to each hair-follicle ; passing from the superficial part of the corium, on 

 the side to which the hair slopes, obliquely downwards, to be attached 

 near the bottom of the follicle (arrector pili, fig. 133, n). When the 

 muscle contracts, the hair becomes erected, and the follicle is dragged 

 upwards so as to cause a prominence on the general surface of the 

 skin ; whilst the part of the corium from which the little muscle arises 

 is correspondingly depressed ; the roughened condition known as 

 * goose skin ' being in this way produced. 



The sebaceous glands (fig. 133, t) are small saccular glands, the 



