ORGANS OF THE SENSES. 499 



appear to be much affected by disease ; it in some cases even 

 being entirely absent. 



It is thickest over the simple papilla), which are usually 

 entirely concealed by it ; over the fungiform and calyciform 

 papillae it is very thin and delicate, while over the filiform 

 papillae it is prolonged into long filiform processes, which cor- 

 respond in number and arrangement with the secondary 

 papilla themselves. (See Plate LlV.jfy. 1, 2.) 



These filiform appendages vary much in length, being very 

 short upon the sides and near the tip of the tongue, but three 

 or four times as long near its centre (see Plate LlV.jtf^. 1, 

 2.) ; at the very tip they are often entirely wanting, the 

 papilla3 in this situation presenting the appearance of large open 

 follicles with slightly spinous rims. (See Plate LV.yzV/. 4.) 



Each filiform process is constituted of flattened epithelial 

 scales, which lie in the direction of their length, and fre- 

 quently contains a canal in its centre. 



Tubular nerve filaments, terminating in loops, have been 

 discovered in the fungiform and filiform papillae, but not 

 hitherto in either the simple or calyciform papillae, although 

 nerve filaments, in some form or other, doubtless exist in these 

 also. 



The internal minute structure of the three principal forms 

 of compound papillae requires a careful and searching examin- 

 ation, with a view to the determination of their respective 

 functions. From a consideration of their outward configura- 

 tion, they would all appear to be well adapted to receive 

 gustatory impressions. The fungiform papillae seem to be so 

 by their prominence and the delicacy of the epithelium by 

 which they are invested, the calyciform papillae also by the 

 tenuity of their epithelial covering and by their cupped form, 

 and the filiform papillae, by reason of the cavity which oc- 

 cupies the centre of each, and the regular disposition of the 

 secondary papillae around this. 



An additional, and to my mind, indeed, an almost con- 

 clusive reason in favour of the subserviency of the filiform 

 papillae to the reception of gustatory impressions, is derived 

 from the consideration that they cover mneteen~t\ventieths of 



