THE INTERNAL EAR 693 



while the remaining portions of the anterior surface and the whole 

 of the inferior margin are entirely membranous. Closely associated 

 with the auditory tube are the tensor and, levator palati muscles, lying 

 laterally and ventrally to the tube. These muscles serve also as dilators 

 for the tube. 



VASCULAR SUPPLY 



The Blood-vessels. The mucosa of the middle ear is richly sup- 

 plied with blood-vessels, the larger of which lie in the deeper part of the 

 membrane and supply capillary vessels to the tunica propria. The blood- 

 vessels of the auditory tube are especially numerous. 



In the tympanic membrane the arteries and veins form an annular 

 plexus at the margin; and a group of similar vessels surrounds the 

 manubrium mallei, lying in the deeper layers of the cutaneous portion 

 of the membrane. 



The mucosa of the tympanum is peculiar in the relative deficiency 

 of capillary vessels (Prussak, 1869) ; the veins are numerous. The 

 veins of the auditory tube empty into the internal jugular; they also 

 communicate with the cavernous sinus by a trunk of considerable size 

 (Bench, 1895). 



The lymphatics of the middle ear form plexuses in the connective 

 tissue of the mucosa and in a general way follow the course of the 

 smaller veins. They lead in part to the lymphatic nodes behind the ear, 

 and in part to the parotid group (Kolliker). They also communicate 

 with the perilymphatic spaces of the internal ear. 



THE INTERNAL EAR 



GENERAL CONSIDERATIONS 



The internal ear includes a series of membranous structures together 

 with the terminal fibers of the acoustic nerve ; these are contained within 

 a series of connected cavities hollowed out of the petrous portion of 

 the temporal bone, and in relation with the mesial wall of the tympanum. 

 The central portion of this bony cavity, an ovoid space, is known as 

 the vestibule; its outer wall presents the orifice of the fenestra vestibuli 

 which leads to the tympanum, but during life is closed by the base of 

 the stapes. Opening from the vestibule, at one end, are the bony cavi- 

 ties occupied by the three semicircular canals which, in a general way, 



