MAMMALIA. 703 



(824.) The structure of the spinal cord and the origins of the 

 spinal nerves throughout all the Mammalia are precisely similar, 

 and exactly correspond with what occurs in the human body ; nei- 

 ther does the anatomical distribution of the individual nerves de- 

 rived from this source require any special notice, since, generally 

 speaking, it differs in no important particular from the arrangement 

 with which every anatomist is familiar. 



(825.) The sense of touch in Mammalia is diffused over the 

 whole surface of the body ; its perfection in different parts being 

 of course influenced by the nature of the integument, and the 

 number of sentient nerves appropriated to any given region. All 

 the nerves derived from the sensitive tract of the spinal medulla, 

 and the three divisions of the fifth pair of encephalic nerves, are 

 equally susceptible of tactile impressions ; so that, in a class so 

 extensively distributed as that before us, we need not be sur- 

 prised to find a special apparatus of touch developed in very 

 different and remote parts adapted to particular exigencies. Thus 

 the whiskers of the Seals and of nocturnal Carnivora, the lips of 

 the Horse, the trunk of the Elephant, the hands of Man, the hind 

 feet of the Quadrumana, and even the extremity of the tail 

 where that organ is prehensile, are all in turn made available as 

 tactile instruments, and exercise the sense in question with the 

 utmost delicacy. 



In the Bats, where the sense of vision becomes inadequate to 

 guide them through the dark recesses where they lurk, that of 

 touch assumes its utmost developement, and every part of the 

 body that could by possibility be furnished with it has been 

 abundantly provided for in this respect. Not only is the broad 

 expanse of the wing acutely sensible, but the very ears have been 

 converted into delicate feelers ; nay, from the tip of the nose in 

 some species, membranes of equal sensibility have been largely 

 developed, so that the Bats, as was ascertained by Spallanzani, even 

 when deprived of sight and hearing, will fly fearlessly along, and 

 avoid every obstacle with wonderful precision, guided apparently 

 by the sense of touch alone. 



(826.) The sympathetic system of the Mammifera differs in no 

 important particular from the human, the arrangement of the gan- 

 glia and the distribution of the plexuses being in all respects the 

 same. 



(827.) In the conformation of the genito-urinary apparatus in 

 Mammalia the physiologist will find many circumstances of ex- 

 treme interest. 



