618 THE EAR 



part of the membrane and supply capillary vessels to the tunica 

 propria. The blood vessels of the Eustachian tube are especially 

 numerous. 



In the tympanic membrane the arteries and veins form an an- 

 nular plexus at the margin ; and a group of similar vessels sur- 

 rounds the manubrium mallei, lying in the deeper layers of the 

 cutaneous portion of the membrane. 



The inucosa of the tympanum is peculiar in the relative defi- 

 ciency of capillary vessels (Prussak*) ; the veins are numerous. 

 The veins of the Eustachian tube empty into the internal jugular ; 

 they also communicate with the cavernous sinus by a trunk of 

 considerable size (Dench f). 



The lymphatics of the middle ear form plexuses in the connec- 

 tive 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 J). They also 

 communicate with the perilymphatic spaces of the internal ear. 



THE INTERNAL EAR 



The internal ear includes a series of membranous structures 

 together with the terminal apparatus of the eighth cranial nerve ; 

 these are contained within a series of connected cavities hollowed 

 out of the petrous portion of the temporal bone, they are in rela- 

 tion 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 ovalis which leads to 

 the tympanum, but during life is closed by the base of the stapes. 

 Opening from the vestibule, on the one hand, are the bony cavities 

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

 project from the dorsal aspect of the vestibule ; on the other hand 

 the bony cochlea containing its series of spiral canals projects 

 anteriorly from the vestibule. Collectively these spaces, with sev- 

 eral diver ticula, form the bony labyrinth, and within them in life 

 are contained a number of membranous sacs whose general form 

 corresponds more or less closely to that of the bony cavity ; these 

 sacs collectively form the membranous labyrinth. 



The vestibule contains two of these membranous sacs, the sac- 

 cule and the utricle, which are connected by means of the slender 



* Arch, f . Ohrenheilk., 1869. f Diseases of the Ear, 1895. 



% Handbuch, III. 



