THE SENSE OF HEARING. 



811 



M 



cessus Folianus, long and slender, arises from an eminence just below the 

 neck of the malleus, and, passing forward and outward, is inserted in the 

 Glaserian fissure in the wall of the tympanum. The malleus is held in posi- 

 tion partly by ligaments ; the suspensory or superior ligament passes downward 

 and outward from the roof of the tympanum to be inserted into the head of 

 the malleus. The main portion of the anterior ligament is attached to the 

 neck of the malleus just above the processus graeilis ; it embraces the latter, 

 and, passing forward, finds its origin 

 in the anterior wall of the tympanum 

 and in the Glaserian fissure. Another 

 division of this ligament, the external 

 ligament, arises and is attached more 

 externally than that just described. 

 The ligaments of the malleus serve to 

 keep its head in position. The exter- 

 nal ligament, being attached above the 

 axis of rotation of the hammer, pre- 

 vents the head of this bone from 

 moving too far inward, and the manu- 



brium from being pushed too far outward. The superior ligament, owing to 

 its oblique course, restrains the head of the hammer from moving too far 

 outward. 



The incus, ambos, or anvil-bone (Fig. 273) is shaped somewhat like a bicus- 

 pid tooth. Its thicker portion is hollowed on the surface and is covered with 



cartilage for articulation with the 

 head of the malleus. It has two 

 processes, a long and a short, 

 which project at right angles to 

 -2 ~ 



Ig.inc 



FIG. 272. Ligaments of the ossicles and their axis 

 of rotation (from Foster, after Hensen). The figure 

 represents a nearly horizontal section of the tym- 

 panum, carried through the heads of the malleus 

 and incus : if, malleus ; I, incus ; t, articular tooth 

 of incus ; Ig.a and Ig.e, external ligament of mal- 

 leus ; Ig.inc, ligament of the incus ; the line a-x rep- 

 resents the axis of rotation of the two ossicles. 



FIG. 273. The incus of the right side : A, anterior face ; B, 

 Internal face (after Testut) : 1, body of incus ; 2, processus 

 brevis ; 3, processus longus ; 4, articular surface for the mal- 

 leus ; 5, a convex tubercle, processus lenticularis, for articu- 

 lation with stapes ; 6, rough surface for attachment of the 

 ligament of the incus. 



FIG. 274. The stapes (after Testut) : 1, 

 base ; 2, anterior crus ; 3, posterior crus ; 

 4, articulating surface of head of the 

 bone ; 5, cervix or neck. 



each other ; the former has a length of 4| millimeters, and the latter a length 

 of 3 to 3J millimeters. When in position the long process descends nearly 

 parallel with the manubrium, but it has less than three-fourths the length of 

 the latter. The free end of the long process is turned sharply inward at right 

 angles, and terminates in a round projection, the os orbiculare, which is provided 

 with cartilage for articulation with the head of the stapes. The short process is 



