1298 THE SKIN, MAMMARY GLANDS AND DUCTLESS GLANDS 



with relatively large lumina in the coils and narrow short ducts, and occur only 

 in the external acoustic (auditory) meatus. 



They are very abundant on the dorsal and superior part of the acoustic meatus in the region of 

 the cartilaginous part, where in the adult most of them open on the surface of the skin close to 

 hairs. Others open into the hair follicles as they all do in the fa?tus and child. Their secretion, 

 the cerumen, is, when freshl}- secreted, a fluid or semifluid oily material of a yellowish-brown 

 colour, which on exposm-e to the air becomes sohd like wax. 



The sebaceous glands [gl. sebaceae] are simple branched or unbranched 

 alveolar glands distributed over nearly the whole surface of the body. Nine- 

 tenths of them are closely associated with the hairs, into the follicles of which 

 they empt}' (figs. 1050, 1051), and are therefore absent from certain of the non- 

 hairy parts of the body, as the flexor surfaces of the hands and feet, the dorsal 

 surfaces of the distal phalanges of the fingers and toes. On the other hand, a few 

 are found, usually much modified, opening independent of the hair follicles, as 

 at the angles of the red margins of the lips, around the nares, around the anus, 

 and the tarsal (Meibomian) glands in the eyelids. Modified sebaceous glands 

 are also found upon the mammary papilla and areola in the female, and in some 

 cases upon the superficial surface of the glans and the surface of the prepuce of 

 the penis, here known as preputial glands ; also a few very small ones may be found 

 upon the labia minora, the glans and prepuce of the clitoris. 



The glands vary in size in different situations and also in individuals and races. They 

 range from .2 to 2.2 mm. long and nearly as broad. Among the smallest are those of the scalp. 

 The largest are found on the alae of the nose and on the cheeks where their ducts are visible to 

 the unaided eye. They are also large on the mons pubis, labia majora, scrotum, about the anus 

 and on the mammary areola. Smaller glands are also found associated with these large ones. 

 The size of the glands is independent of the size of the hairs with which they are associated but 

 the number of glands depends upon the size of the hair. On small hairs one or more glands are 

 always found and on large hairs there may be a whole wreath of from four to six separate glands 

 opening into the hair folhcle. 



The number of sebaceous glands has never been exactly estimated, although, it is known 

 that they are less numerous than the sudoriferous glands. This is very evident on the extrem- 

 ities, trunk, and neck, where they bear a relation of 1 to 6 or 8. On the scalp, concha of the ear, 

 and skin of the face thej^ are about equal in number while on the forehead, ala3 of the nose, free 

 borders of the eyehds and external genital organs in the female the number of sebaceous glands 

 is greater than the number of sudoriferous glands. 



Each sebaceous gland consists of a secretory portion, the body, connected with 

 the hair follicle or the surface of the skin by a wide short duct. In the small 

 glands, the body of the gland may consist of a single alveolus but in the larger 

 glands there are from four to twenty of these connected by irregular ducts to a 

 single excretory duct. 



The ducts open into the hair follicles near their necks between the inner root sheath and the 

 hair or upon the surface of the skin. They are always very short, cylindrical, or infundibuli- 

 form, and their epithelium is directly connected with that of the outer root sheath of the hair 

 folhcle or with the epidermis where the hair is wanting. 



The glands lie in the superficial layers of the corium and where one or a few are connected to 

 a single hair, they usually open into the hair follicles on the side toward which the hairs point. 

 Where there are several glands for one hair they may completely surround the hairs like a rosette. 



The cells of the body of the gland and of the duct are surrounded by a basement membrane 

 outside of which is a connective-tissue sheath, both of which are continuous with corresponding 

 coverings of the hair follicle. 



The periphery of the alveolus is formed of small cubical epithelial cells, the central part of 

 larger and more rounded cells. The cells of the alveolus show all stages of fatty degeneration, 

 the peripheral cells contain small fatty particles, those nearest the centre larger and more nu- 

 merous fat droplets, some of them being completely broken down. There is no distinct lumen to 

 the alveolus but this is filled with degenerated cells, fatty particles and debris of broken-down and 

 cast-off cells. The deeper cells continue to multiply and push the more superficial cells toward 

 the lumen where they in turn are cast off. The secretion thus formed is known as the sebum 

 cutaneum. It is a whitish or whitish-yellow mass composed of fat and broken-down cells of the 

 consistency of thick oil which spreads over the sm-facc of the skin and hair as a lubricant. 

 Through the decomposif ion of its fat more or less ()(h)ur is produced. When the gland duct is 

 blocked the secretion is retained and I)ecomes more solid and is known as a comedo. The active 

 .secretion of the sebaceous glands does not begin l)cfore the fifth or sixth year of life. It attains 

 its maximum in the adult and decrea.ses in the aged. 



The relation of the arrcctores pilorum to tlie scl)aceous glands has been described in con- 

 nection with the relation of these muscles to the hairs. 



Vessels and nerves. — The sebaceous glands are surrounfled by a fine capillary plexus of 

 blood-vessels clo.scly associated with those of the hairs and skin. Concerning their lymph- 

 vessels little is knf)wn. The nerves of the sebaceous glands are connected with those of the 

 skin and hair but the exact manner of distribution is not clearly understood.! 



