810 



DISSECTION OF THE EAR. 



processes, 

 short 



and long. 



Stapes : 

 base; 



head 



neck ; and 

 crura. 



articulate with the malleus. The short process (c) is somewhat 

 conical, and projects backwards nearly horizontally ; its extremity 

 rests against the lower and inner part of the margin bounding the 

 opening into the mastoid antrum. The long process (d) is almost 

 vertical, and descends parallel to the handle of the malleus, behind 

 and internal to which it lies : it diminishes towards the extremity, 

 where it is bent inwards, and ends in a small flattened knob the 

 orbicular process (), for articulation with the stapes. 



The STAPES (fig. 298) has a base or wider portion, and a head 

 with two sides or crura, like a stirrup. The base (d) is directed 

 inwards, and is a thin osseous plate, convex at the upper margin 

 and nearly straight at the lower, corresponding with the shape of 

 the fenestra ovalis, into which it is received : the surface turned to 

 the vestibule is convex, while the opposite is excavated. The 

 head (a) is marked at the extremity by a superficial depression 

 which articulates with the orbicular process of the incus ; and it is 

 supported on a slightly constricted part, the neck (b). The crura 

 extend horizontally from the neck to the base, and are grooved on 

 the surface towards the enclosed aperture ; the anterior cms (c) is 

 shorter and straighter than the posterior. 



The bones 

 have two 

 sets of liga- 

 ments ; 

 either to 

 unite one to 

 another 

 by joints, 



or to fix 

 them to the 

 tympanic 

 wall. 



Ligaments 

 of malleus 

 are superior, 

 anterior, 



and 

 external. 



One band to 

 incus, 



and one to 



stapes. 



Membrane 

 in aperture 

 of stapes. 



LIGAMENTS OF THE OSSICLES. The small bones of the tympanic cavity are 

 united into one chain by joints, and are farther kept in position by ligaments 

 fixing them to the surrounding wall. 



Joints of the bones. Where the ossicles touch, they are connected together 

 by articulations corresponding with the joints of larger bones ; for the osseous 

 surfaces are covered with cartilage, are surrounded by a thin capsular liga- 

 ment of fibrous tissue, and lubricated by a synovial sac. One articulation of 

 this nature exists between the head of the malleus and the incus, and a second 

 between the orbicular process of the incus and the head of the stapes. 



Union of the bones to the wall. The bones are kept in place by the reflec- 

 tion of the mucous membrane over them, and by the following ligaments, 

 three being connected with the malleus, and one each with the incus and 

 stapes : 



Ligaments of the malleus. The superior or suspensory ligament is a 

 slender band which descends from the roof of the tympanum to the head of 

 the malleus. The anterior ligament is the strongest of all : it passes from the 

 foi-e part of the neck of the malleus to a projection at the anterior margin of 

 the notch of Kivinus. and to the sides of the Grlaserian fissure. A part of this 

 ligament entering the fissure has been described as a muscle under the name 

 of laxator tympani. The external ligament is short and fan-shaped : its fibres 

 radiate from the outer and posterior parts of the neck of the malleus to the 

 edge of the notch. 



The ligament of the incus attaches the extremity of the short process of 

 that bone to the tympanic wall at the lower part of the orifice of the antrum 

 mastoideum. 



The annular ligament of the stapes is composed of very short fibres, which 

 unite the circumference of the base of the stirrup to the margin of the 

 fenestra ovalis. 



Special ligament of the stapes. Closing the interval between the crura of 

 the stapes there is a very thin membrane which is attached to the groove of 

 the bone. It is covered above and below by the mucous membrane. 



Two 



MUSCLES OF THE OSSICLES (fig. 299). Two muscles are connected 

 with the chain of bones, one being attached to the malleus, the 

 other to the stapes. 



