252 our POSTS OF THE INTELLIGENCE SERVICE 



regulating the action of the le\'er, as the force which fibres exert 

 upon the handle of the malleus increases, aniphtude of movement 

 of that bone diminishes. In this way, the special form of the 

 drum-head secures a maximum of efficiency for tones of the feeblest 

 intensity " (M'Kendrick). 



Briefly, energy applied to the membrane is passed on to the 

 handle of the malleus diminished in amplitude but with increased 

 intensity. 



(b) Ossicles. The three bones of the middle ear — the malleus, 

 the incus and the stapes — stretch across the tympanic cavity 

 forming an articulated chain of levers, so that every normal move- 

 ment of the tympanic membrane is transmitted by the stapes to 



-SUPERIOR. LIGAMENT OF^MALLEUS 



ANTERIOR LIGAMENT OF MALLEU5 



i^ORT PROCESS <y 

 POSTERIOR LIGAMENT 

 OF INCUS 



LONG PROCESS OF 1NCU5 



EMINEtlTIA PYRAMIDAL15 

 TO WHICH THE TEMDON OF 

 M. STAPEDIUS IS ATTACHED 



^=^S= M. TENSOR TYMPANI 



^^ SEPTUM CANALIS 

 MUSCULOTUBARII 



MANUBRIUM MALLE.I 



Fig. 64. — Diagram of the left Membrana Tympani and Chain of Tympanic Ossicles 

 seen from the medial aspect. 



The line A — B is the axis of rotation of the malleus and inciis. The dotted line represents 

 the line of leverage applied from the handle of the malleus to the posterior ligament of 

 the incus. The stapes lies almost at right angles to the plane of the paper. 



the fluid of the internal ear. The Malleus, or hammer, is about 

 18-19 mm. long, and has an average weight of 23 mg. It consists 

 of a thickened rounded head and a long handle — the manubrium, 

 which is attached to the tympanic membrane, the tip of the 

 handle reaching the miibo. Near the insertion of the head and 

 handle arises a bony process — the processus gracilis or processus 

 Folianus, which projects forward and is continued by a ligament, 

 the anterior ligament by means of which the hammer is anchored 

 to the wall of the tympanum. There is also a shorter protuberance, 

 the processus brevis, which presses against the edge of the upper 

 surface of the drum. Three other ligaments are attached to the 

 malleus, the external ligament, binding it to the external face 

 of the tympanic cavity, the superior or suspensory ligament, 

 attaching the top of the head to the roof of the cavity, and the 

 posterior ligament. These ligaments prevent the malleus from 



