Fig. 48. — Examples of different modes of ending of sensory nerve fibres 

 of the frog. 



A, Cells from the olfactory epithelium. B, cells from the retina. C, cells from one 

 of the patches of sensory epithelium in the labyrinth, with which the fibres of 

 the auditory nerve are connected. £>, a portion of the epidermis, showing the 

 ending of a nerve fibre. 



D is ordinary stratified epithelium. A , B, and C are true sensory epithelia — forms of 

 columnar epithelium adapted to the purposes of special senses. In these latter 

 there can be distinguished sense cells and supporting cells. The sense cells bear 

 processes of various kinds on the surface of the epithelium, and at their other ends 

 come into relation with nerve fibres. In A the sense cell is prolonged into a fibre 

 which runs in one of the olfactory nerves as a non-medullated nerve fibre (p. 94). 

 In B also the sense cells are prolonged into fibres, though these are connected 

 with the nerve by the intermediation of other cells with whose processes their fibres 

 interlock. In C, on the other hand, the sense cells are not continued into fibres, 

 but are embraced'by branches of nerve fibres belonging to cells in the ganglion of 

 the auditory nerve. Thus they resemble D, where the nerve fibres have a similar 

 relation to the cells of the epithelium. In the lower animals, such as the 

 earthworm, the sensory nerve endings in the skin are usually of the type of A' 

 and B, rather than that of C and D. 



cn. t Cone; n.c, nerve cells; n./. t nerve fibres; rd. t rod; s.c, sense cells; st.c, 

 supporting cells. 



89 



