532 



THE SKIN AS AN EXTERNAL COVERING. 



work surrounding the convolution. This bears a remarkable re emblance to the 

 network forming the glomerulus in the Malpighian capsule of the kidney. Finally, 

 a plexus of nerves passes to the glands. 



The total number of sudoriferous glands may be about two and one-half 

 millions, representing a secretory superficies of approximately 1080 square 

 meters. With respect to their function, it should be borne in mind that they 

 secrete sweat. Nevertheless, an oily fat is admixed with their secretion, possibly 

 from special cells, and this may predominate in the secretion in animals, as in 

 the hoof-glands of the frog of a horse's foot, the glands on the sole of the dog's 

 foot, and those of birds' feet. Meissner attributes only a secretion of fat to the 

 convoluted glands, and Unna also believes that the sweat is produced from the 



intercellular spaces of the prickle-cells, which 

 communicate with the penetrating sweat- 

 / ducts. 



Tubular and reticular lymphatics without 

 valves (Fig. 178, 1, v) are present in the cutis, 

 in part with blind terminations in the papillae. 

 Neumann observed them arranged in the form 

 of a network about the hair-follicles and their 

 glands. A coarser network of larger lymph- 

 trunks is found in the subcutaneous tissue. 



The blood-vessels appear principally in 

 two layers; namely, in a superficial layer, 

 from which the loops for the cutaneous papillae 

 arise; and a deep subcutaneous layer. Both 

 vascular areas anastomose by means of pro- 

 cesses. In addition, the glands of the skin are 

 surrounded by a network of vessels. 



THE SKIN AS AN EXTERNAL 

 COVERING. 



It is the function of the subcutaneous 

 fatty tissue to fill the depressions be- 

 tween the different parts of the body, as 

 well as to round off projecting portions, 

 so that the rounded fulness of the body- 

 form, agreeable to the eye, results. The 

 fatty tissue acting as a soft cushion, also 

 affords protection from excessive pres- 

 sure, as on the sole of the foot, in the 

 palm of the hand, on the buttocks; and 

 it encloses various more important parts 

 that may be readily injured, as, for in- 

 stance, the vessels and nerves in the 



axilla, the inguinal fold, and the popliteal space. As a poor con- 

 ductor of heat, the subcutaneous fat shields the body against ex- 

 cessive loss of heat ; the cutis vera and the epidermis exert a similar 

 influence The firm, elastic, readily movable cutis is capable of afford- 

 ing protection against external mechanical injuries, and in this it is 

 aided by the epidermis, whose dry, impervious, horny tissue, without 

 nerves and vessels, is especially adapted to afford protection against 

 poisons in solution; and is capable of offering considerable resistance 

 even to thermic and chemical influences. A thin layer of sebum pro- 

 tects the free surface of the epidermis from maceration by fluids and 

 from the destructive action of the air. The epidermal layer is, further, 

 important in the fluid-economy of the body. It exerts pressure upon the 

 cutaneous capillaries, and thus affords protection against excessive loss 



FIG. 183. Sebaceous Gland with a Lanugo- 

 hair: a, glandular epithelium; b, rete 

 Malpighii. continued into the glandular 

 epithelium; c, fat-containing cells and 

 free fat as glandular contents; d, acini; 

 e, root sheath with the hair. 



