188 THE AUDITORY OSSICLES. [BOOK in. 



anteriorly (Figs. 167, 171 Ig.a.), the anterior ligament, embraces 

 the long or Folian process, the other, the exterior ligament 



Ig.inc 



lg.e 

 FIG. 171. THE LIGAMENTS OF THE OSSICLES. (After Hensen.) 



The figure represents a nearly horizontal section of the tympanum, carried through 

 the heads of the malleus and incus. 



M. malleus. 7. incus, t. articular tooth of incus. Ig. a. anterior and Ig. e. external 



ligament of the malleus. Ig. inc. ligament of the incus. 

 The line ax represents the axis of rotation of the two ossicles. 



(Fig. 171 Ig.e.), is placed more externally ; the two are nearly 

 continuous, leaving however a distinct gap (Fig. 171) between 

 them. They serve to limit the movements of and so to keep in 

 place the head of the malleus, which it is said still remains in 

 position even after the incus has been removed. 



The joint between the malleus and incus, which like other 

 joints has articular cartilages, synovial membrane, a capsule and 

 ligaments, the latter being very slender, is of a peculiar shape, the 

 lower part of the articular surface of each bone projecting in the 

 form of blunt teeth (Figs. 164, 170, 171, 173, t). These teeth 

 lock into each other in such a way that when by an inward 

 movement of the tympanic membrane the malleus is carried in- 

 wards, the incus is necessarily carried inwards also, but that when 

 the malleus is moved outwards, that is towards the external 

 passage, the incus does not necessarily follow it. Hence while 

 every inward movement of the tympanic membrane leads to an 

 inward movement of the malleus, incus and stapes, in succession, 

 the three falling back into their previous positions when the 

 movement ceases, should the tympanic membrane for any reason 

 be pushed unduly outwards into the meatus, the joint between the 

 malleus and incus gapes and so prevents the stapes being pulled 

 out of the fenestra ovalis. 



A ligament, ligament of the incus (Fig. 171 Ig. inc.), more or 

 less divisible into two parts, passing from the median wall of the 

 tympanum to the end of the short process of the incus, firmly 

 secures that part of the chain of ossicles. The long process of 

 the incus hangs nearly vertically downwards but its end turning 

 c harply round at right angles expands into a flattened knob, 

 which, covered with cartilages, forms a joint with the cartilage 

 covered head of the stapes (Figs. 164 B' and D, 172). 



The foot of the stapes (Fig. 172), an irregularly oval plate of 

 bone, covered on the side towards the internal ear with cartilage, 



