612 MANUAL OF HISTOLOGY. 



Their appearance is the same as that of the terminal filaments of the 

 gustatory cells. Fusion with the latter fibres has not been yet observed, 

 however. The hidden position of the gustatory buds within the narrow 

 grooves formed by the elevations of the papillae seems to have some signi- 

 ficance in regard to the persistence of after-taste sensations. 



The mode of termination of the nerves of the papilla* fungiformes is 

 not so well known. Loven states that he has found a gustatory bud in the 

 centre of the crown of each in the rat. Krause also mentions the same. 



A few years ago some points of interest in regard to what we now 

 know to be similar structural relations in the tongue of the frog were 

 put forward by Key. 



The tongues of frogs, namely, present, besides a narrower form of papilla, 

 another broader species, reminding us of the p. fungiformes of mammals. 

 On these we can better study the structural arrangement of such parts. 



The side walls of these broad papillae are clothed with columnar cells, 

 the edges of the crown with ciliated epithelia. The surface itself of the 

 crown, on the other hand, is covered by one of the other varieties of 

 epithelial elements destitute of cilia. In the first place, columnar cells 

 are to be seen giving off processes below, which anastomose with one 

 another, forming thus a kind of network in which here and there im- 

 bedded nuclei may be recognised. 



But between these cylinder cells, and at different heights, smaller roundish 

 or elliptical elements present themselves, with relatively large nuclei. 

 Each of these gives off both above and below a process ; the first ascends 

 to the free surface between the columnar epithelial elements in the form 

 of a slender rod, while the process extending downwards into the mucous 

 membrane is but an extremely delicate filament, on which minute vari- 

 cosities may be recognised characteristic of the finest nerve fibrillae. 



In the axis of each papilla is a nervous twig, consisting of a few broad 

 medullated tubes. At the end of the twig the latter axis cylinders split 

 up into very delicate filaments, likewise varicose. They resemble greatly 

 the end filaments of the last species of cell mentioned, and, according 

 to Key's statement, may be seen to be directly connected with the latter. 



With some show of reason, this coating of the crown of the papillae of 

 the frog's tongue has been compared to a superficially unfolded gustatory 

 bud of the mammal. But more recent investigation by Englemann has 

 put the correctness of this comparison again in question, and has revealed 

 to us a greater amount of complexity in structure here than was at first 

 suspected. This observer notices, in addition to his "bowl-cells" (the 

 " cylinders"), the rod-bearing structures of Key, to which he gives the 

 name of " cylinder cells," and whose nervous nature he denies, as also that 

 of the bowl cells. Besides these, he speaks of another peculiar set of 

 elements, however, branching both above and below, which he calls 

 " forked cells," and which he regards as the terminal structures of the 

 gustatory nerves, with whose axis- cylinders the ultimate ramifications of 

 their inferior processes are continuous. 



306. 



The organ of smell, to the consideration of which we now pass on, 

 consists, as is well known, of the two nasal fossce and accessory cavities 

 in connection with the latter. Besides being a sensory apparatus, this 

 organ also serves as a passage for the respiratory system, and a canal for 

 the reception of the tears. 



