ULTRASTRUCTURE AND HISTOPH YSIOLOG Y OF MEMBRANES 13 



three large endings (Sy) each of which is in contiguity with the mem- 

 branes of at least two receptor cells (Tr). Figure 15 is a higher 

 magnification of a large fiber synaptic junction demonstrating some of the 

 cytological details characteristic of this type of ending. Note that the 

 synaptic membranes do not show any thickening characteristic of other 

 synapses (de Lorenzo, 1959-62). However, " synaptic vesicles " are con- 

 sistently seen (Figs. 1 1, 14 and 15). On the other hand, the small fibers end 

 in yet another fashion. They remain in their receptor membrane mesaxons 

 throughout their course and terminate in individual receptors rather than 

 sharing two or more receptor cells. They do not contain large numbers 

 of vesicles as do the large fibers, but instead contain a few mitochondria 

 and punctate fibrils which seem to exhibit a periodicity when seen in 

 longitudinal sections. Like the large fibers, their membranes have no 



Potf 



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F'brcbia- ■ ' otiagen 



Text-fig. IIL Schematic representation of the ultrastructure and organiza- 

 tion of the taste buds in the papilla foliata of the rabbit. 



