898 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



likewise distributed over the entire surface of the body, and here, also, is 

 perhaps more highly developed in the tentacles or pseudopods which are 

 so often found. 



In fishes projecting organs at the side of the buccal opening receive 

 terminations of afferent nerves, and these, together with the fins, may be 

 regarded as especially developed tactile organs, although here, also, the 

 entire body surface possesses general sensibility. ' 



In reptiles no special tactile organ is present, unless the tongue, in 

 certain instances, may fulfilFthis function. 



In birds the tactile sensibility of the skin must be to a certain ex- 

 tent interfered with by the thick coating of feathers and the sensibility 

 of the feet by the dense scales which usually cover these parts. In birds 

 in general it is the beak which possesses tactile sensibility in the highest 

 degree. 



In mammals the greatest variation exists in the specialization of 

 certain parts of the body for the appreciation of tactile sensations. In 

 monkeys, although four hands may be said to be present, they are not to 

 be regarded as sensitive organs as are the hands of man ; since, in the 

 first place, their fingers do not possess the power of separate movement 

 and their thumb is much shorter and incapable of being brought into 

 apposition with the fingers ; while the palm of the hand, which frequently 

 serves as a means of progression, is covered with calloused epithelium. 

 In certain monkeys with prehensile tails this organ is doubtless possessed 

 of tactile power in the highest degree. 



In solipedes, ruminants, and carnivora, in whom the extremities of 

 the limbs terminate in a single or double hoof, in claws, or calloused 

 skin, in these localities the sense of touch must be very imperfect. But 

 these parts of the animal body must be capable, nevertheless, of giving 

 distinct notions as regards resistance, solidity, and consistence, since 

 these horny parts rest on a highly developed papillary layer of the derm. 

 In solipedes and ruminants, especially in the former, the lips possess a 

 considerable degree of mobility, and are, as has been shown, the princi- 

 pal organs of prehension and are highly endowed with tactile sensibility. 

 In carnivora the termination of the soft parts about the anterior nares is 

 extremely sensitive and is employed by them as a tactile organ, while it 

 is only a step farther to the hog or the elephant, where the prolongation 

 of this part of the body acquires extreme perfection as an organ of 

 tactile sensibility. In certain animals the long hairs growing from the 

 upper lip, as in the cat and the rat and the seal, are to be regarded as 

 tactile organs, since they conduct tactile impressions to the sensory 

 nerves. Probably, also, the spines of the porcupine fulfill the same 

 function. 



Like the more specific sensations, the sensations of touch require for 



