274 NORMAL HISTOLOGY. 



of a layer of epithelium containing two sorts of cells: first, ciliated 

 cells, which are somewhat flask-shaped and are called "hair-cells"; 

 second, epithelial cells, the " cells of Deiters," which surround and 

 enclose the hair-cells, except at their free ends, and reach the sur- 

 face of the mucous membrane, where their ends are cuticularized. 

 These cells of Deiters extend from the surface of the membrane to 

 the basement-membrane, while the hair-cells extend only for a por- 

 tion of that distance. 



The dendrites of the auditory nerve are distributed among these 

 cells, but are not in organic union with them (Fig. 257). In this 

 respect the auditory apparatus differs from the olfactory and resem- 

 bles the tactile. The nervous dendrites are processes of bipolar 

 ganglion-cells situated in the ganglia on the branches of the auditory 

 nerve. The neurites from those cells presumably carry the nervous 

 stimuli to the cerebrum. The bipolar cells are, therefore, analogous 

 to the posterior root ganglion-cells of the spinal nerves. Whether 

 this single neuron carries the nervous stimulus directly to the cere- 

 bral cortex cannot be stated, but it is probable that there is an inter- 

 mediate neuron in the tract of transmission, perhaps in the medulla 

 oblongata. 



The external auditory meatus is lined with skin containing compara- 

 tively few papilla;. The ceruminous glands which secrete the wax 

 resemble the sweat-glands of the skin. The deep portions of these 

 coiled tubular glands have a rather wider lumen than the sweat-glands 

 and are lined with a single layer of cubical epithelium containing gran- 

 ules of pigmented material and fat destined to become constituents 

 of the cerumen. The ducts of the glands are lined with a double 

 layer of epithelial cells. Muscular fibres are present in the walls 

 of the glands, the arrangement being similar to that in the sweat- 

 glands. The skin extends over the outer surface of the tympanic 

 membrane, but here the corium is very thin and devoid of papillae. 

 The rete Malpighii is also thin. Beneath this skin, but separated by 

 a thin vascularized layer of areolar tissue, is the tympanic mem- 

 brane, consisting of two layers of fibrous tissue, an outer in which 

 the fibres run radially, and an inner composed of circular fibres. 

 The inner covering of the tympanic membrane is a single layer of 

 flattened epithelium resting on a small amount of vascularized areo- 

 lar tissue. The tympanic cavity (middle ear) is also lined with 

 flattened epithelium in a single layer which passes into ciliated epi- 

 thelium near the opening into the Eustachian tube, likewise lined 



