OSSICLES OF THE TYMPANUM. fci 



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 decreases in size towards its extremity, 

 where it is curved slightly forwards, and flattened from within outwards. 



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

 the eminence below the neck forwards and outwards to the Glaserian fissure, to 

 which it is connected by bone and ligamentous fibres. It gives attachment to 

 the Laxator Tympani. 



The processus brevis is a slight conical projection, which springs from the root 

 of the manubrium, and lies in contact with the membrana tympani. Its summit 

 gives attachment to the Tensor Tympani. 



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. Fig. 380. The Small Bones of the Ear. 



The body is somewhat quadrilateral, but seen from the Outside. (Enlarged.) 

 compressed laterally. Its summit is deeply 

 concave, and articulated with the malleus ; in 

 the fresh state, it is covered with cartilage 

 and 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 backwards, and 

 is attached to the margin of the opening lead- 

 ing into the mastoid cells, by ligamentous 

 fibres. 



The long process-, longer and more slender 



than the preceding, descends nearly vertically behind the handle of the malleus, 

 and, bending inwards, terminates in a rounded globular projection, the os orbi- 

 culare, or lenticular process, which is tipped with cartilage, and articulates with 

 the head of the stupes. In the foetus the os orbiculare exists as a separate bone, 

 but becomes united to the long process of the incus in the adult. 



The /Stapes, so called from its close resemblance to a stirrup, consists of a head, 

 neck, two branches, and a base. 



The head presents a depression, tipped with cartilage, which articulates with 

 the os orbiculare. 



The neck, the constricted part of the bone below the head, receives the inser- 

 tion of the Stapedius muscle. 



The two branches (crura) diverge from the neck, and are connected at their 

 extremities by a flattened, oval-shaped plate (the base), which forms the foot of 

 the stirrup, and is fixed to the margin of the fenestra ovalis by ligamentous 

 fibres. 



Ligaments of the Ossicula. These small bones are connected with each other 

 and with the walls of the tympanum, by ligaments, and moved by small mus- 

 cles. The articular surfaces of the malleus and incus, the orbicular process of 

 the incus and head of the stapes, are covered with cartilage, connected together 

 by delicate capsular ligaments, and lined by synovial membrane. The liga- 

 ments connecting the ossicula with the walls of the tympanum are three in 

 number, one for each bone. 



The suspensory ligament of the malleus is a delicate, round bundle of fibres, 

 which descends perpendicularly from the roof of the tympanum to the head of 

 the malleus. 



The posterior ligament of the incus is a short, thick, ligamentous band, which 

 connects the extremity of the short process of the incus to the posterior wall 

 of the tympanum, near the margin of the opening of the mastoid cells. 



