SKIN 



385 



Epidermis. 



and other special forms. The greater part of the surface of the skin 

 presents many little furrows, the sulci cutis, which intersect so that they 

 bound rectangular spaces. On the palms and soles the furrows are parallel 

 for considerable distances, being separated from one another by slender 

 ridges, the cristce cutis, along the summits of which the sweat glands open. 

 The ridges are most highly developed over the pads of tissue at the finger 

 tips, where they present the familiar spiral and concentric patterns. 

 These pads of connective tissue, the toruli tactiles, must not be confounded 

 with elevations due to underlying muscles. 



In the pentadactylous mammals, each extremity typically presents five digital 

 toruli, at the tips of the fingers or toes; four interdigital toruli, near the metacarpo- or 

 metatarso-phalangeal joints; and two or three proximal cushions a tibial and an 

 elongated fibular; or a radial and two ulnar, one behind the other. Often the inter- 

 digital cushions fuse, as in the paw of the cat and the ball of the human foot, and the 

 one between the thumb and fingers may be suppressed. These toruli are very promi- 

 nent in the embryo. According to 

 Miss Whipple (Zeitschr. f. Morph. u. 

 Anthr., 1904, vol. 7, pp. 261-368) 

 they are primarily walking pads, 

 witfi ridges at right angles to the slip- 

 ping force. Usually they are con- 

 sidered primarily tactile. The ex- 

 tensive literature pertaining to them 

 has been reviewed by Schlagenhaufen 

 (Anat. Hefte, 1906, Abt. II, vol. 15, 

 pp. 628-662). 



Corium. 



Corium. The corium is a 

 layer of densely interwoven 

 bundles of connective tissue ex- 

 tending from the epidermis to 

 the fatty, areolar subcutaneous 

 tissue (Fig. 387). Toward the 

 epidermis the corium forms pa- 

 pilla, which vary considerably in size and number in different parts of the 

 body. They are tallest (even 0.2 mm. high) and most numerous, often 

 being branched, in the palms and soles. Beneath the epidermal ridges 

 they may occur quite regularly in double rows (Fig. 388), as long since 

 observed by Malpighi. In the skin of the face the papillae are poorly 

 developed, and in advanced age they may wholly disappear. The papillae 

 are composed of cellular connective tissue, which forms a tunica propria; 

 and each papilla contains a terminal knot of capillary blood vessels, or a 

 tactile corpuscle (Fig. 152, p. 159). The corpuscles are most numerous 

 in the sensitive finger tips, where they may be found in one papilla in 

 every fur. 

 25 



Papillae under Tactile 

 the ridge A. corpuscle. 



Papillae under 

 the ridge D. 



PIG. 388. VERTICAL SECTION FROM THE SOLE OF THB 

 FOOT OF AN ADULT, SHOWING FOUR RIDGES (A-D) 

 WITH A PAIR OF PAPILLA BENEATH EACH. Between 

 the papillae of D is the duct of a sweat gland. X 25. 



