370 THE' SKIX AXD THE SENSE-ORGANS. 



occur in the epidermis, but by far the greater quantity of the cuta- 

 neous pigment is found in the cutis, and more especially in the 

 loose layer of branched cells, which form the boundary between 

 epidermis and true cutis. These cells, known as chromatophore- 

 cells, have been carefully investigated by Harless. They play an 

 extremely important part in bringing about the well-known 

 changes in the colouring of the skin. Bimmerman has proved 

 that these cells are influenced by stimulation of the nerves 

 supplying- the region in which they occur. Ehrmann has been 

 able to trace a direct connection between the nerve-fibres and 

 the pigment-cells (Fig. 231 I, II). In such cases the pigment was 

 sometimes sharply marked off, at others was gradually lost alon<>' 

 the nerve.] 



c. The papillae and ridges of the skin are classified by Leydig 

 as follows: (i) Small ridges, (2) larger ridges, (3) papillae with 

 touch-bodies, (4) papillae without touch-bodies, (5) papillae with the 

 ducts of glands, (6) capillaries in the form of papillae, (7) small 

 elevations, including the lateral organs. 



[All these structures are derived from the cutis, the epithelium 

 above simply repeating the elevation, and being itself either not 

 increased in thickness or only to a slight degree. (For further 

 description of some of these papillae, see Organs of Tactile Sensation, 

 p. 380.) 



Peculiar wart-like papillae are found on the articulations of the 

 first phalanges with the metatarsus, on the same articulations and 

 on the articulations between the first and second phalanges of the 

 third and fifth toes, and on the articulations between the first, 

 second, and third phalanges of the fourth toe. These papillae are 

 connected with the long flexor tendons by fine tendinous bands 

 (Klein). 



Temporary papillae are developed in the females of H 'ana temporaria during the 

 breeding season ; according to O. Huber (/. c.), who has described them, their distri- 

 bution and structure is as follows : 



During the breeding season the skin of the sides of the trunk of female specimens 

 of Rana temporaria is rough ; the small elevations, to which this roughness is due, 

 are each about the size of the head of a pin, and have the appearance of small, 

 rounded, white or pale rose-coloured, warty growths. The papillae reach their 

 greatest development and are most numerous on the sides of the trunk (Fig. 232 I) ; 

 they may be traced on to the tympanic membrane, where they are arranged in a ring, 

 and in some cases under the eyes to the sides of the snout. 



Anteriorly the papillae are absent from the median portion of the dorsal surface of 

 the trunk, but posteriorly, behind a line joining the anterior extremities of the two 

 iliac bones, the papillae cover the whole surface. 



