134 THE SENSE OF TOUCH IN ANIMALS 



of skin to be very prominent, and in many of them more so 

 than the papillary ridges or papillae of the corium. But in 

 considering the sense of touch which resides in the hand and 

 foot of mammals, these structures can only be looked upon 

 as of secondary importance, and their function and meaning 

 will be discussed later. Most of the sections show that each 

 of these ridges of the under-surface of the epidermis, which 

 Blaschko and Miss Whipple have called Driisenleisten, because 

 of their relation to sweat-glands, corresponds to a papillary ridge, 

 on which the duct opens, and they are very generally pigmented, 

 from their close relation to the rete mucosum of the epidermis. 



The following four general rules are illustrated from the 

 cases brought forward : 



(1) Differentiation of the papillary ridges, or their equivalents, 

 and the papillae of the corium, increases with the higher develop- 

 ment of the species examined. (By the term " their equiva- 

 lents " is meant the series of epidermic modifications, scales, 

 epidermic warts, and rods which are functionally similar to the 

 ridges, but of lower development.) 



(2) The degrees of development of the papillary ridges and 

 the papillae of the corium are closely related to one another. 



(3) The greatest development of the papillary ridges is 

 shown by height, clearness of outhne, and regularity of the 

 ridges, and by the presence in certain areas of imbrication of 

 the ridges, distal or proximal. 



(4) The greatest development of the papillae of the corium 

 is shown by the acuteness of their angles, and their approxima- 

 tion to the free surface of the epidermis, and closeness to one 

 another. 



(1) Among the Monotremes and Marsupials the epidermic 

 modifications are simple, as in Figs. 53, 54 of the former, and 

 57, 58, 59, 62, 63, 64, 66 to 72 of the latter. But the Tasmanian 

 wolf, Fig. 57, has more highly developed papillae of the corium 

 than many higher forms. The two species of Macrojms, Figs. 

 74, 75, and Fig. 73 of J^pyprymnus rufescens, have very 

 highly developed papillae of the corium, and marked epidermic 

 nodules or warts. But of all the Marsupials (eight), only 



