THE SKIN. 137 



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 horizontal 

 section. 



The hairs of animals are often curiously marked by the arrangement 

 of their medulla, the markings being characteristic of particular 

 species. 



Muscles of the hairs. A small muscle composed of bundles of plain 

 muscular tissue is attached to each hair-follicle (arrector pili, fig. 156, n) ; 

 it passes 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 to a projection formed by a localised hypertrophy of the 

 outer root-sheath. 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 pro- 

 duced. 



The sebaceous glands (fig. 156, t) are small saccular glands, the 

 ducts from which open into the mouths of the hair-follicles. Both the 

 duct and the saccules are lined by epithelium, which becomes charged 

 with fatty matter. This sebaceous matter is discharged into the cavity 

 of the saccule, probably owing to the disintegration of the cells within 

 which it is formed. There may be two or more sebaceous glands 

 attached to each follicle. 



The sebaceous glands are developed as outgrowths from the outer 

 root-sheath (fig. 161, s). 



The sweat-glands are abundant over the whole skin, but they are 

 most numerous on the palm of the hand and on the sole of the foot. 

 They are composed of coiled tubes, which lie in the deeper part of the 

 integument and send their ducts up through the cutis to open on the 

 surface by corkscrew-like channels which pierce the epidermis (fig. 153, 

 p. 130). 



The glandular or secreting tube is a convoluted tube composed of a 

 basement-membrane lined by a single layer of cubical or columnar 

 epithelium-cells, and with a layer of longitudinally or obliquely 

 disposed fibres between the epithelium and basement-membrane. These 

 fibres are usually regarded as muscular, but the evidence on this point is 

 not conclusive. The secreting tube is considerably larger than the efferent 

 tube or duct, which begins within the gland and usually makes several 

 convolutions before leaving the gland to traverse the cutis vera. The 

 efferent tube has an epithelium consisting of two or three layers of 

 cells, within which is a well-marked cuticular lining, but there is no 



