712 THE ORGANS OF SENSE. 
divergent fangs. It consists of a body (corpus incudis), a long process (crus longum), 
and a short process (crus breve); the two processes form with each other an angle of 
90° to 100°. The body and short process are situated in the epitympanic recess. 
The body presents a more or less saddle-shaped surface for articulation with the 
head of the malleus. This surface is directed forwards, and its lower part is 
hollowed out for the accommodation of the cog-tooth of the malleus. In front of 
this hollow it is prominent and spur-like. The short process is thick, triangular 
in shape, and projects horizontally backwards ; its conical extremity, covered with 
cartilage, articulates with the fossa incudis in the postero-inferior part of the 
epitympanic recess. The long process projects, almost perpendicularly, downwards 
from the body into the tympanic cavity, where it lies parallel with, but 14 mm. 
behind and internal to, the handle of the malleus. Its lower end is bent inwards 
and narrowed to form a short neck, on the inner extremity of which is a small knob 
of bone, the processus lenticularis, for articulation with the head of the stapes. 
Until the sixth month of fcetal life, this process exists as a separate ossicle, termed 
the os orbiculare. 
The stapes (Fig. 519, E) presents a head (capitulum stapedis), a neck (collum 
stapedis), two crura (crus anterius et posterius), and a base or footplate (basis 
stapedis). The head, directed outwards, is concave externally, for articulation 
with the processus lenticularis of the incus. The neck is the slightly constricted 
part immediately internal to the head, and from it the two crura spring; the 
tendon of the stapedius muscle is inserted into the posterior aspect of the neck. The 
anterior crus is shorter and less curved than the posterior. Diverging from each 
other, the crura are directed inwards and are attached—one near the anterior, the 
other near the posterior end of the footplate. The footplate almost completely 
fills the oval fenestra, and, like it, is somewhat oval or reniform, its anterior end 
being the more pointed. In the recent condition a membrane fills the arch formed 
by the crura and the footplate, the crura being grooved for its reception. In the 
child the crura of the stapes are less curved than in the adult, and the opening 
bounded by them and the footplate is nearly triangular. 
Articulations of the Tympanic Ossicles.—The joint between the head of the 
malleus and the body of the incus (articulatio incudomalleolaris) is diarthrodial, 
and may be described as one of reciprocal reception. It is surrounded by a capsular 
ligament, from the inner surface of which a wedge-shaped meniscus projects into the 
joint cavity and incompletely divides it. The articulation of the processus lenti- 
cularis and the capitulum stapedis (articulatio incudostapedia) is of the nature of 
an enarthrosis and is surrounded by a capsular ligament. An interarticular carti- 
lage has been described as occurring in this joint, while some observers deny the 
presence of a synovial cavity and regard the articulation as a syndesmosis, the 
articular surfaces being held together merely by fibrous tissue. 
Ligaments binding the Ossicles to the Walls of the Tympanic Cavity (lig. 
ossiculorum auditus),—The malleus is attached to the walls of the tympanum by 
three ligaments (Fig. 520), viz. anterior, superior, and external. The anterior liga- 
ment (lig. mallei anterius) consists of two portions: (a) the band of Meckel, which is 
attached to the base of the processus longus and passes forwards through the 
Glaserian fissure to reach the spine of the sphenoid; it was formerly described as 
the laxator tympani muscle: () a firm bundle of fibres, the lig. mallet anterius of 
Helmholtz, which extends from the anterior boundary of the notch of Rivinus to the 
anterior aspect of the malleus, above the base of the processus longus. The superior 
ligament (lig. mallei superius) extends, almost vertically, from the head of the 
malleus to the roof of the epitympanic recess. The external ligament (lig. mallei 
laterale) is short and fan-shaped; its fibres converge from the posterior half of 
the notch of Rivinus to the crista mallei. The posterior part of this lga- 
ment is strong and constitutes the ligamentum mallet posticum of Helmholtz. It 
forms, together with the ligamentum mallei anterius, the axis around which the 
malleus rotates, and the two constitute what Helmholtz has termed the ‘“ axis-liga- 
ment” of the malleus. 
The posterior extremity of the crus breve of the incus is tipped with cartilage 
and fixed by means of a ligament, the ligamentum incudis posterius (Fig. 520), to the 
