1164 THE ORGANS OF SPECIAL SENSE 



enlarged from the accumulation of pent-up secretion. The largest sebaceous 

 glands are those found in the eyelids the Meibomian glands. 



The Sudoriferous or Sweat Glands (glandulae sudoriferae) (Figs. 868 and 878) 

 are the organs by which a large portion of the aqueous and gaseous materials 

 is excreted by the skin. They are found in almost every part of this structure, 

 being absent on the red border of the lips, the glans penis, and inner surface of 

 the prepuce. On the eyelids they are somewhat modified, and are called ciliary 

 glands (glandulae ciliares [Molli]); about the anus they are extremely large, and 

 are called circumanal glands (glandulae circumanales). The sweat glands are 

 situated in small pits below the under surface of the corium, or, more frequently, 

 in the subcutaneous areolar tissue, surrounded by a quantity of adipose tissue. 

 They are small, lobular, reddish bodies, consisting of a single convoluted tube, 

 from which the efferent duct (ductus sudoriferus) proceeds outward through the 

 corium and cuticle, becomes somewhat dilated at its extremity, and opens on the 

 surface of the cuticle by an oblique valve-like aperture (porus sudoriferus). The 

 duct, as it passes through the epidermis, presents a spiral arrangement, being 

 twisted like a corkscrew, in those parts w r here the epidermis is thick; where, 

 however, the epidermis is thin, the spiral arrangement does not exist. In the 

 superficial layers of the corium the duct is straight, but in the deeper layers it is 

 convoluted or even twisted. The spiral course of these ducts is especially distinct 

 in the thick cuticle of the palm of the hand and sole of the foot. The size of the 

 glands varies. They are especially large in those regions where the flow of perspi- 

 ration is copious, as in the axillae, where they form a thin, mamillated layer of a 

 reddish color, which corresponds exactly to the situation of the hair in this region; 

 they are large also in the groin. Their number varies. They are most numerous 

 on the palm of the hand, presenting, according to Krause, 2800 orifices on a square 

 inch of the integument, and are rather less numerous on the sole of the foot. In 

 both of these situations the orifices of the ducts are exceedingly regular, and open 

 on the curved surface ridges. In other situations they are more irregularly 

 scattered, but the number in a given extent of surface presents a fairly uniform 

 average. In the neck and back they are least numerous, their number amounting 

 to 417 on the square inch (Krause). Their total number is estimated by the same 

 writer at 2,381, 248, and supposing the aperture of each gland to represent a surface 

 of -g-y^ of an inch in diameter, he calculates that the whole of these glands would 

 present an evaporating surface of about eight square inches. Each gland consists 

 of a single tube intricately convoluted, terminating at one end by a blind extremity, 

 and opening at the other end upon the surface of the skin. The wall of the duct 

 is thick, the lumen seldom exceeding one-third of the diameter of the tubes. The 

 tube, both in the gland and where it forms the excretory duct, consists of two 

 layers (except in the epidermis, where the epithelium of this layer forms the wall) 

 an outer, formed by fine areolar tissue, and an inner layer of epithelium. The 

 external coat is thin, continuous with the superficial layer of the corium, and extends 

 only as high as the surface of the corium. The epithelial lining in the distal 

 part of the coiled tube consists of a single layer of cubical cells, supported on a 

 basement membrane. Between the epithelium and the fibrocellular coat lies a 

 layer of longitudinally or obliquely arranged involuntary muscle fibres, the con- 

 traction of which aid in the expulsion of the sweat. In the proximal part there 

 are two or more layers of polyhedral cells lined on the internal surface (next the 

 lumen of the tube) by a delicate membrane devoid of muscle fibres. The contents 

 of the smaller sweat glands is quite fluid; but in the larger glands the contents 

 are semifluid and opaque, and contain a number of colored granules and cells 

 which appear analogous to epithelial cells. 



The bloodvessels are branches from the subcutaneous vessels and the arterial plexus of the 

 deep part of the corium. Numerous amyelinic nerve fibres lie upon the membrana propria of a 

 sweat gland. From them fibrils pass inward and terminate by end bulbs upon the cells of the gland. 



