THE ORGANS OF THE SPECIAL SENSES. 267 



These arc situated in the corium, the former lying in some of the 

 papillae projecting into the rete mucosnm. 



The tactile corpuscles are of two forms, differing slightly from 

 each other in structure : first, those of Meissner, and, second, those 

 of Krause. 



The tactile corpuscles of Meissner (Fig. 249) consist of a group 

 of epithelial cells closely associated with the teledendrites of a 

 nerve-fibre. The cells are closely compacted together to form an 

 ellipsoid body. The nervous dendrite, with its medullary sheath, 

 enters this body at one of its ends, and, after making one or two 

 spiral turns around the mass of epithelial cells, loses its medullary 

 sheath and breaks up into a number of teledendrons, which are dis- 

 tributed among the epithelial cells. The neurilemma and the 

 endoneurium of the fibre are continued over the corpuscle, consti- 

 tuting a species of capsule. 



The tactile corpuscles of Krause (Fig. 250) possess a capsule 

 composed of delicate fibrous tissue, covered and lined with endo- 

 thelial cells. The dendrite of the nerve-fibre loses its medullary 

 sheath upon penetrating this capsule, and then breaks up into tele- 

 dendrites, that form a complex tangle within the cavity of the cor- 

 puscle. There appear to be no cells among the teledendrites, the 

 interstices being occupied by lymph. These corpuscles are espe- 

 cially abundant in the conjunctivae and the edges of the eyelids, 

 but occur also in the lip, large intestine, posterior surface of the 

 epiglottis, and the glans penis and clitoris. They may receive 

 dendrites from more than one nerve. Those of Meissner are found 

 throughout the skin, being most abundant where the tactile sense is 

 most acute. 



The Pacinian corpuscles (Fig. 251) are large oval bodies, com- 

 posed of a number of concentric cellular lamellae, surrounding a 

 central, almost cylindrical cavity, and covered externally with a 

 layer of endothelioid cells, which appear to be continuous with the 

 delicate endoneurium of the fibre. The latter enters the corpuscle 

 at one of its ends, soon loses its medullary sheath, and is finally 

 subdivided into a number of teledendrites within the central cavity. 



The "genital corpuscles" which are found in the glans of the 

 penis and that of the clitoris are similar in structure to the Pacinian 

 corpuscles, but the lamellar envelope of the latter is here reduced to 

 one or two ill-developed lamellae. 



The nervous impulses inaugurated in the tactile and Pacinian 



