HISTOLOGY 



137 



97C). Epithelial sensory cells may be grouped in small clusters forming 

 specialized sense organs. Such are the sense organs of the lateral-Hne 

 system of fishes and amphibians (Fig. 98) 

 and the "taste buds" in the mouth of higher 

 vertebrates (Fig. 99). 



The essential layer of the internal ear 

 is derived from embryonic ectoderm. This 

 auditory epithehum produces sensory cells 

 in localized groups which become the special 

 sensory organs of the ear, the maculae and 

 cristae acusticae (Fig. gjA). The organ of 

 Corti in the spiral cochlea of the mammalian 

 ear is a highly specialized sensory epithelium. 



The retina of the vertebrate eye is pro- 

 duced by outgrowth from the wall of the 

 embryonic forebrain and consists of two 

 ectodermal epithelia (Fig. 60). The outer 

 is a simple pigmented and non-nervous epithelium. The inner is 

 the most complex of all sensory epithelia, all the cells at its outer 

 surface becoming the sensory rods and cones, while the deeper cells 

 become speciahzed as nerve cells arranged in two layers intervening 



Fig. 98. — Sense organ of 

 the lateral line of the amphib- 

 ian, Triturus (Diemyctylus). 

 c, cone cells; s, spindle cells. 

 (From Kingsley, Comparative 

 Anatomy of Vertebrates; after 

 Kingsbury.) 



Sustentacular Pore Gustatory 

 cell canal cell 



Gustatory Pore Sustentacular 

 cell canal cell 



Connective tissue 

 of tunica propria 



Fig. 99. — Taste-buds from a vallate papilla of the human tongue; as seen in section 

 perpendicular to the surface of the epithelium. 5 is a diagrammatic representation 

 of the structure of one "bud." X47S. (From Morris, Human Anatomy.) 



between the rod and cone layer and the optic nerve (Fig. loo). The epithe- 

 lial nature of the adult retina is obscured by the fact that the original open 

 space between the outer pigmented epithehum and inner sensory epithe- 

 lium is obliterated, thus bringing the two epithelial surfaces into close 



