296 ORGANS OF THE SENSES. 



density of the tongue, and the horny prehensile or masti- 

 cating organs which often cover its surface in higher classes, 

 we can perceive distinct gustatory villi on that of the ce- 

 phalopods and the cold-blooded vertebrata, which are suc- 

 ceeded by larger papillae and calyces in the birds and 

 mammalia. These highly vascular and sensitive papillae 

 which terminate the gustatory filaments of the fifth pair of 

 nerves gradually assume the arrangement and forms which 

 they present on the human tongue as we ascend through the 

 quadrumana to man. 



SIXTH SECTION. 



Organs of Touch. 



The most general sense in animals is that of touch, of 

 which all the others may be mere modifications, and it is 

 situate in the highly vascular and sensitive surface of the 

 skin which covers and protects the entire machine. This 

 general sense relates to the most common physical properties 

 of bodies, as their form, their consistence and their tem- 

 perature, without some perception of which animals 

 could scarcely provide for their own subsistence or the con- 

 tinuance of their race. It constitutes the simplest form of 

 an organ of sense, where the minute cutaneous vascular 

 papillae are scarcely yet apparent, which form by their 

 development on the ends of sensitive nerves the more com- 

 plicated organs of the higher senses ; and the contact of 

 the outward object, required in all, is most obvious in 

 this sense. As the sensitive surface of the skin, the vascular 

 layer of the corium, exudes upon its exterior an insensible 

 and extra-vascular cuticle and rete mucosum, which vary 

 much in their thickness, and in the nature and quantity of 

 the materials which often consolidate them, the effect of 

 external impressions in exciting perceptions of touch must 

 chiefly depend on the structure and sensibility of the parts 

 touched and on the general condition of the nervous system 

 in animals. Those invertebrated animals therefore, of each 

 class, which have their exterior naked and soft, will have a 

 more general and acute sense of touch than such allied forms 

 as have their bodies covered with dense substances, although 

 in the latter animals the higher development of the other 



