856 



THE ORGANS OF SPECIAL -SENSE. 



lary, which ramifies beneath the cuticular layer and from the stylo-mastoid branch 

 of the posterior auricular and tympanic branch of the internal maxillary, which 

 are distributed on the mucous surface. The superficial veins open into the exter- 

 nal jugular ; those on the mucous surface drain themselves partly into the lateral 

 sinus and veins of the dura mater and partly into a plexus on the Eustachian tube. 

 The membrane receives its nervous supply from the auriculo-temporal branch of 

 the inferior maxillary, the auricular branch of the vagus, and the tympanic branch 

 of the glosso-pharyngeal. 



Ossicles of the Tympanum (Fig. 459). 



The tympanum is traversed by a chain of movable bones, three in number, the 

 malleus, incus, and stapes. The first is attached to the mernbrana tympani, the 

 last to the fenestra ovalis, the incus being placed between \the two, and is con- 

 nected to both by delicate articulations. 



The Malleus, so named from its fancied resemblance to a hammer, consists of a 

 head, neck, and three processes the handle or manubrium, the processus gracilis, 

 and the processus brevis. 



The head is the large upper extremity of the bone ; it is oval ki shape, and 

 articulates posteriorly with the incus, being free in the rest of its extent. The 

 facet for articulation with the incus is constricted near the middle, and is divided 

 by a ridge into an upper, larger, and lower, lesser part, which form nearly a right 

 angle with each other. Opposite the constriction the lower margin of the facet 

 projects in the form of a process, the cog-tooth or spur of the malleus. 



The neck is the narrow contracted part just beneath the head ; and below this 

 is a prominence, to which the various processes are attached. 



The manubrium is a vertical process of bone, which is connected by its outer 

 margin with the membrana tympani. It is directed downward, inward, and back- 

 ward ; it decreases in size toward its extremity, where it is curved slightly forward, 

 and flattened from within outward. On the inner side, near its upper end, is a 

 slight projection, into which the tendon of the Tensor tympani is inserted. 



The processus gracilis is a long and very delicate process, which passes from 

 the eminence below the neck forward and outward to the Glaserian fissure, to 



which it is connected by ligamentous fibres. 

 In the foetus this is the longest process of the 

 malleus, and is in direct continuity with the 

 cartilage of Meckel. 



The procesaus brevis is a slight conical pro- 

 jection, which springs from the root of the 

 manubrium ; it is directed outward, and is 

 attached to the upper part of the tympanic 

 membrane. 



The Incus has received its name from its 

 supposed resemblance to an anvil, but it is 

 more like a bicuspid tooth, with two roots, 

 which differ in length, and are widely separated 

 from each other. It consists of a body and 

 two processes. 



The body is somewhat quadrilateral but compressed laterally. On its anterior 

 surface is a deeply concavo-convex facet, which articulates with the head of the 

 malleus ; in the fresh state it is covered with cartilage and the joint lined with 

 synovial membrane. 



The two processes diverge from one another nearly at right angles. 

 The short process, somewhat conical in shape, projects nearly horizontally 

 backward, and articulates with a depression, the fossa mcudis, in the lower and 

 back part of the epi tympanic recess. 



The long process, longer and more slender than the preceding, descends nearly 



Processus brevis.. 



Stapes. 



Os orbiculare. 



Head. 



Crura. 



FIG. 459. The small bones of the ear, 

 seen from the outside. (Enlarged.) 



