THE ORGANS OF SPECL\L SENSE 579 



pigment granules. They have long narrow duels lined with a two- 

 layered epithelium. In children these ducts open into the hair 

 foUicles; in the adult they open on the surface near the hair follicles. 

 The secretion of these glands plus desquamated epithehum consti- 

 tutes the ear wax. In the bony portion of the canal the skin is thin, 

 free from glands and hair, and hrmly adherent to the periosteum. 



The tympanic membrane (ear drum) separates the external ear 

 from the middle ear. It consists of three layers: a middle layer or 

 substantia propria, an outer layer continuous with the skin of the 

 external ear, and an inner layer continuous with the mucous mem- 

 brane of the middle ear. 



The substantia propria consists of closely woven connective-tissue 

 fibres, the outer libres having a radial direction from the head of 

 the malleus, the inner fibres having a concentric arrangement and 

 being best developed near the periphery. 



The outer layer of the tympanic membrane is skin, consisting of 

 epidermis and of a thin non-papillated corium, excepting over the 

 manubrium of the malleus, where the skin is thicker and papillated. 



The inner layer is mucous membrane and consists of a stroma of 

 fibro-elastic tissue covered with a single layer of low epithelial cells. 



Blood-vessels. — Blood is supplied to the tympanic membrane by 

 two sets of vessels, an external set derived from the vessels of the 

 external auditory meatus and an internal set from the vessels of the 

 middle ear. These give rise to capillary networks in the skin and 

 mucous membrane, respectively, and anastomose by means of perfo- 

 rating branches at the periphery of the membrane. From the capil- 

 laries the blood passes into two sets of small veins, one extending 

 around the periphery of the membrane, the other following the handle 

 of the malleus. 



Lymphatics.^ — These follow in general the course of the blood- 

 vessels. They are most numerous in the outer layer. 



Nerves. — The larger nerves run in the substantia propria. From 

 these, branches pass to the skin and mucous membrane, beneath the 

 surfaces of which they form plexuses of fine fibres. 



The INIiDDLE Ear 



The middle ear or tympanum is a small chamber separated from 

 the external ear by the tympanic membrane and communicating with 

 the pharynx by means of the Eustachian tube. Its walls are formed 



