CHAPTER 11 



SUJIMARY 



An extensive series of facts has here been brought together in 

 connection with the skin-structm."es of the ventral surface of the 

 mammahan hand and foot. There is found on tliis surface a 

 speciahsed form of sldn, not only in the character of the epi- 

 dermis, but also of the corium, and in both cases, extreme varia- 

 bihty has been shown to occur in the different groups of mammals, 

 and the variabihty of the corium in a few birds examined has 

 also been shown to be considerable. The seven coarser modi- 

 fications of the outer layers of the epidermis have been shortly 

 described and sub-varieties of these also mentioned, but the 

 chief interest of the free epidermic surface hes in the highest 

 development of these modifications in the form of papillary ridges. 

 Remarkable and complex patterns are shown to be formed of 

 these ridges, the complexity increasing very closely according 

 to the higher organisation of the animals in question. There 

 are differences of view as to the nomenclature suitable for the 

 various epidermic structures, especially the ridges, and these 

 differences of view of course depend upon the main function, or 

 fimctions, which are attributed to the ridges, but it seems difficult 

 to resist the large mass of evidence in favour of the intimate and 

 essential connection of these ridges with the papillary layer of 

 the corium, and consequently with the sense of touch. They 

 are, therefore, frankly associated with their function and still 

 called papillary ridges. This is not to underrate or ignore such 

 secondary uses as they may have in affording a roughened 

 surface for the hand and foot in prehension and walking and m 

 raising the mouths of the sudoriparous ducts so rendering the 

 flow of moisture over the surface more free. In the corium 



