1135 



ANTERIOR 

 CRUS 



GROOVE FOR 



OBTURATOR 



MEMBRANE 



OF STAPES 



POSTERIOR 



CRUS 



QASE OF STAPES 



The short process (crus breve), somewhat conical in shape, projects almost 

 horizontally backward, and articulates with a depression, the fossa incudis, in the 

 lower and back part of the epitympanic recess. 



The long process (crus longum), longer and more slender than the preceding, 

 descends nearly vertically behind and parallel to the handle of the malleus, and, 

 bending inward, terminates in a rounded globular projection, the os orbiculare or 

 lenticular process (processus lenticularis), 

 which is tipped with cartilage, and 

 articulates with the head of the stapes. 

 In the fetus the os orbiculare exists as 

 a separate bone. 



The Stapes (Fig. 845), so called from 

 its close resemblance to a stirrup, con- 

 sists of a head, neck, two crura, and a 

 base. A 



The head (capitulum stapedis) pre- FlG 845 ._ The rig ht stapes (enlarged). A. Viewed 

 sents a depression, tipped with cartilage, from above. B. Medial view. (Spaitehoiz.) 



which articulates with the os orbiculare. 



The neck, the constricted part of the bone succeeding the head, receives the 

 insertion of the Stapedius muscle. 



The two crura (crus anterius and crus posterius) diverge from the neck and are 

 connected at their extremities by a flattened, oval-shaped plate, the base (basis 

 stapedis), which forms the foot-plate of the stapes and is fixed to the margin of 

 the fenestra ovalis by ligamentous fibres. The foot-plate almost fills the oval 

 window (Fig. 834). Of the two crura, the anterior is shorter and less curved 

 than the posterior. In a recent specimen a membrane will be observed filling 

 the space between the crura and the foot-plate. This membrane is connective 

 tissue and is called the membrana obturatoria stapedis. The stapes lies practically 

 horizontal. 



Articulations of the Ossicles of the Tympanum (articulationes ossiculorum auditus) (Fig* 

 840). These small bones are connected with each other and with the walls of the tympanum by 

 ligaments, and are 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 by cartilage, con- 

 nected by delicate capsular ligaments and lined by synovial membrane. 



Ligaments Connecting the Ossicula with the Walls of the Tympanum dig. ossiculorum 

 auditus). The malleus is fastened to the wall of the tympanum by three ligaments the 

 anterior, superior, and external ligaments. 



The anterior ligament of the malleus (tig.' mallei anterius) 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 prolonged through the fissure 

 to reach the spine of the sphenoid. 



The superior ligament of the malleus (lig. mallei superius) is a delicate round bundle of 

 fibres which descends perpendicularly from the roof of the epitympanic recess to the head of the 

 malleus. It is sometimes called the suspensory ligament. 



The external ligament of the malleus (lig. mallei laterale) is a triangular plane of fibres passing 

 from the posterior part of the notch in the tympanic ring to the head of the malleus. The mal- 

 leus rotates around an axis composed of the external and anterior ligaments, hence these two 

 ligaments constitute what Helmholtz called the axis ligament of the malleus. 



The incus is fastened to the wall of the tympanum by two ligaments, the posterior and the 

 superior. 



The posterior ligament of the incus (lig. incudis posterius) is a short, thick, ligamentous band 

 which connects the extremity of the short process of the incus to the posterior and lower part of 

 the epitympanic recess, near the margin of the opening of the mastoid cells. 



A superior ligament of the incus (lig. incudis superius) has been described, but it is little 

 more than a fold of mucous membrane. 



The vestibular surface and the circumference of the base of the stapes are covered by hyaline 

 cartilage, and the annular ligament of the stapes (lig. annulare baseos stapedis) connects the 

 circumference of the base to the margin of the fenestra ovalis. 



