THE SWEAT-GLANDS. 489 



completely surrounds a hair-sac on all sides, constituting a glandu- 

 lar rosette. 



The sebaceous glands grow after birth. In fact, those of the 

 labia minora do not exist at all at birth. 



The composition and uses of the sebaceous secretion are specified 

 on page 227. 



3. The Sudoriferous or Sweat- Glands. These consist of a single 

 delicate convoluted tube, which secretes the sweat. They occur on 

 the whole surface of the skin, except the concave side of the con- 

 cha of the ear, and the external auditory meatus, the glans penis, 

 the inner lamella of the prepuce, and a few other localities and 

 open upon it by numerous fine apertures. 



Each sweat-gland may be divided into the gland proper and the 

 excretory duct. (Figs. 138, 317, 321.) The proper gland is rounded 

 or elongated, yellowish, or yellowish-red, and H \ to 5 V f an i nc ^ 

 in diameter. On the eyelids, however, and some other parts, they 

 are only T i ? of an inch ; while on the areola they are ^ of an inch, 

 and in the hairy parts of the axilla even ^ to J of an inch thick, 

 and T 1 ^ to j- of an inch broad. They are mostly lodged in the 

 deeper layer of the corium, sometimes more superficially, and often 

 in the subcutaneous areolar tissue among the hair-sacs. 



Number of the Sweat- Glands. Krause states that in a square inch 

 of the skin there are between 400 and 600 glands on the back of 

 the trunk, the cheeks, the upper arm, and the thigh; 924 to 1,090 

 on the anterior part of the trunk, on the neck, brow, forearm, back 

 of the hand, and foot; 2,685 on the sole of the foot; and 2,736 on 

 the palm of the hand. Their total number, including those of the 

 axilla, is estimated at 2,381,248 ; and their volume, including the 

 latter, 39,653 cubic inches. 



The aggregate length of all the excretory ducts of the sweat-glands 

 in the body has been estimated by Wilson 1 at 28 miles. 



1. In their minute structure, the sweat-glands usually consist of 

 a single canal, pretty uniform in diameter throughout its length 

 (which Krause once found to be ^ of an inch), twined into a coil, 

 and terminating on the surface on the interior of the latter in a 

 slightly enlarged blind extremity. (Fig. 138.) Most of these, having 

 thin walls, possess an external investment of embryonic collagenous 



1 Treatise on Diseases of the Skin. 



