1498 



HUMAN ANATOMY. 



The stapes (stirrup), as its name implies, is stirrup-shaped and consists of a head, neck, 

 two crura and a base or foot-plate. The external surface of the small rounded head is hollowed 

 out for articulation with the orbicular process of the incus. Just below this is the constricted 

 neck, from which the two crura diverge to become attached to the foot-plate near its lower 



Fig. 1257. 



Head. 



Anteriot crus 



Upper edge 



Posterior 

 Lower edge 



Foot-plate 

 Right stapes, A, seen from above; B, mesial surface of foot-plate. X 4}^. 



margin. The anterior crus is shorter and straighter than the posterior, both being slightly 

 curved. The foot-plate consists of a lamina of bone and corresponds to the bean-shape of the 

 oval window, into which it nearly fits. The upper edge of the foot-plate is convex ; its lower 

 edge is almost straight, being slightly hollowed out near its middle. 



Articulations of the Ossicles. — In the malleo-incudal joint, both articular surfaces are 

 covered with a thin layer of hyaline cartilage. The fairly well-developed capsular ligament, 

 reinforced mesially, is fastened to the depressed margins of the articular surfaces. A wedge- 

 shaped meniscus of fibro-cartilage projects from the upper wall of the capsule between the sur- 



FiG. 1258. 



faces of hyaline cartilage. "When the 

 manubrium handle moves inward, its 

 lower cog catches the corresponding cog 

 of the incus and the long process of the 

 latter must follow. If the handle moves 

 outward, the lower cog moves away 

 from the incus and the latter moves but 

 little" (Politzer). 



The articulation of the incus and 

 stapes is a very delicate but true joint. 

 Both the slightly convex surface of the 

 orbicular process of the incus and the 

 slightly concave surface of the head of 

 the stapes are covered with hyaline car- 

 tilage and united by a capsular ligament 

 made up largely of elastic fibres and 

 thickened on the posterior surface. 

 Sometimes a meniscus of fibro-cartilage 

 separates the two articular surfaces. 



The articulation of the stapes and 

 oval window is effected by the margins 

 of the window and the foot-plate of the 

 stapes. These surfaces, as well as the 

 vestibular aspect of the stapes, are cov- 

 ered with a layer of hyaline cartilage. 

 The cartilage of the foot-plate and that 

 of the window are connected by a liga- 

 ment of elastic fibres, forming a syn- 

 chondrosis. 



In addition to the ligaments con- 

 cerned in the foregoing articulations, 

 four bands attach the ossicles to the tym- 

 panic walls and prevent their excessive 



Frontal section passing through malleus and tympanic membrane, movement; of these, three COnnect the 

 X 8. Drawn from preparation made by Dr. Ralpli Butler. malleUS and one the inCUS 



1. The superior ligament of the malleus extends from the tegmen tympani to the head of 

 the malleus. (Figs. 1252 and 1258.) 



2. The anterior ligament of the malleus is a strong, broad, fibrous band arising from the 

 anterior part of the head and neck of the malleus. Some of its fibres are attached to the ante- 

 rior end of the annulus tympanicus (spina tympanica major) and other fibres pass through the 

 Glaserian fissure to become attached to the spine of the sphenoid. These fibres correspond to the 

 remains of the embryonic process of Meckel of the malleus and envelop the processus gracilis. 



Sup. ligament 



Head of malleus 

 External ligament 

 Mem. flaccida or 

 Shrapnell's membrane 

 Prussak's space 

 Neck 



Short process 



Chorda tympani 



Tendon of tensor 

 tympani 



Handle 



artilage 

 Epidermis 

 Membrana propria 



Mucous membrane 



Membrana tensa 



.\nnulns tendinosus 



