Tin: miPA.\rjf. 919 



inner side, near its upper end. is a slight projection, into which the tendon of the 

 Tensor tympani is inserted. 



The processes 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 bone and ligamentous fibres. 



The pro<-> **>/> bt'i'-'-i* is a slight conical projection which springs from the root 

 of the manubrium. and lies in contact with the membrana tympani. 



The Incus lias 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 the anterior 

 surface of its summit is a deeply concavo-convex facet, which articulates 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 Ssj^ ^^j&~\ P/.,. fc^m*. 



shape, projects nearly horizontally backward, 

 and is attached to the margin of the opening 

 leading into the mastoid cells by ligamentous 



fibres. o.. m TV* n 



7 . , , , JjEJ-Osorbicularc. 



Ihe long process, longer and more slender 

 than the preceding, descends nearly verticallv 

 behind and parallel to the handle of the mal- 



, i i i- i FIG. 545. The small bones of the ear, seen 



lens. and. bending inward, terminates in a from the outside. (Enlarged.) 

 rounded globular projection, the os orbiculare, 



or lenticular ////' .<x. which is tipped with cartilage and articulates with the head 

 of the stapes. 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 insertion of the Stapedius muscle. 

 The two brain-In-* (i-rura] diverge from the neck, and are connected at their ex- 

 tremities 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 muscles. 

 The articular surfaces of the malleus and incus and 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 ligaments con- 

 necting the ossicula with the Avails of the tympanum are four in number two for 

 the malleus, one for the incus, and one for the stapes. 



The anterior li-jament of the malleus was formerly described by Sommerring as 

 a muscle (Laxator tympani). It is now, however, believed by most observers to 



- : >t of ligamentous fibres only. It is attached by one extremity to the neck 

 of the malleus, just above the processus gracilis, and by the other to the anterior 

 wall of the tympanum, close to the Glaserian fissure, some of its fibres being pro- 

 longed through the fissure. 



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. 



The annular ligament of the stapes connects the circumference of the base of 

 this bone to the margin of the fenestra ovalis. 



