GENERAL REMARKS ON THE SENSES. 



OUE studies in embryology have taught us that all the vari- 

 ous forms of end-organs are developed from the epiblast, and 

 so may be regarded as modified epithelial cells, with which are 

 associated a vascular and nervous supply. These end-organS' 

 are at once protective to the delicate nerves which terminate in 



Fig. 371 — Papillse of skm of palm of hand (after Sappey) A vascular network in all 

 cases, and in some nerves and tactile corpuscles, enter the papillse. 



them, and serve to convey to the latter peculiar impressions 

 which are widely different in most instances from those residt- 

 ing from the direct contact of the nerve with the foreign body. 

 All are acquainted with the fact that, when the epithelium is 

 removed, as by a blister, we no longer possess tactile sensibility 

 of the usual kind, and experience pain on contact with objects ; 

 in a word, the series of connections necessary to a sense-percep- 

 tion is broken at the commencement. 



Seeing that all the end-organs on the surface of the body 

 have a common origin morphologically, it would be reasonable 

 to expect that the senses would have much in common, espe- 

 cially when these organs are all alike connected with central 

 nervous cells by nerves. As a matter of fact, such is the case, 



