GLANDS. 425 



tcrnal surface, and far outnumbering the sebaceous glands, 

 which have a somewhat similar distribution. 



They consist of convoluted tubes of nearly equal diameter, 

 which unite, at irregular intervals, with each other, forming 

 looped meshes, all of which terminate in a single excretory 

 duct. (See Plate LVILjft/. 4.) 



The excretory duct is either straight or coiled spirally, and 

 it always terminates in a raised and rounded mammillary pro- 

 cess, evident on the surface of the epidermis. (See Plate 

 XXIII. Jig. 1.) It is straight where the epidermis which it 

 has to pass through is thin, and where, in consequence, its 

 course to the surface is short ; on the other hand, it is coiled 

 in spires which are remarkable for their extreme regularity, 

 where this membrane is thick, as in the palms of the hands 

 and soles of the feet (see Plate XXIV. fig. 3.), and where 

 as a result its course is prolonged. The acting cause which 

 determines this spiral arrangement is probably the gradual 

 flattening to which the outer and older layers of epidermic 

 cells are continually subject from pressure. 



The duct of the sudoriferous glands is formed by an inver- 

 sion of , the epidermis itself, similar to that which forms the 

 lining of the hair follicles. The sudoriferous glands never 

 open into the hair follicles, but in the intervals between them 

 and also between the sensory papilla with which the true skin 

 is covered. 



The palms of the hands and soles of the feet, being entirely 

 free from the sebaceous glands, are occupied exclusively with 

 the sudoriferous ; they are placed in lines or rows, which are 

 variously curved, and which correspond with the arrangement 

 of the sensory papillae of the true skin. The apertures of the 

 sudoriferous glands on the ridges of the skin are just perceptible 

 with the naked eye, but they become very evident and con- 

 spicuous with a lens of moderate power. (Plate XXI ^.fig. 1 . ) 



The secreting cells of the sudoriferous glands are small. 



The tubes are formed like those of the testes of a nucleated 

 variety of fibro-elastic tissue, and are surrounded by a similar 

 plexus of capillaries. These vessels, as well as the tubes 

 themselves, are held in position by bands of fibrous tissue. 



