THE SMALL BONES OF THE TYMPANUM 



79 



The small bones of the tympanum. — These bones, the malleus, incus and 

 stapes, are contained in the upper part of the tj-mpanic cavit\'. Together they 

 form a jointed column of bone connecting the membrana tympani with the 

 fenestra vestibuli. 



The malleus. — This is the most external of the auditory ossicles, and lies in relation with the 

 tympanic membrane. Its upper portion, or head, is lodged in the epitympanic recess. It is 

 of rounded shape, and presents posteriorly an elliptical depression for articulation with the 

 incus. Below the head is a constricted portion or neck, from which three processes diverge. 

 The largest is the handle or manubrium, which is slightly twisted and flattened. It forms an 

 obtuse angle with the head of the bone, and lies between the membrana tympani and the 

 mucous membrane covering its inner surface. The tensor tympani tendon is inserted into the 

 manubrium near its junction with the neck on the medial side. 



Fig. 99. — The Boxes of the Ear. (Modified from Henle.) 



Malleus 



Stapes 



Fossa for incus 



Short process 



Anterior eras 



Base 



Posterior cms 



Head of malleus 



Lateral process 

 Anterior process 



Manubrium 



Articular surface for malleus 



Long process 



Lenticular process 



Base of stapes 



Neck 



The anterior process (processus graciUs or Folii) is a long, slender, deUcate spicukim of bone 

 (.rarelv seen of fiill length except in the fcetus), projecting nearly at right angles to the anterior 

 aspect of the neck, and extending obliquely downward. It hes in the petro-tympanic fissure, 

 and in the adult usually becomes converted into connective tissue, except a small basal stump. 

 The lateral process is a conical projection from the. lateral aspect of the base of the manu- 

 brium. Its apex is connected to the upper part of the tympanic membrane, and its base receives 

 the lateral Ugament of the malleus. The malleus also gives attachment to a superior hgament 

 and an anterior ligament, the latter of which was formerly described as the laxator tympani 

 muscle. • i II 



The incus. — This bone is situated between the malleus externally and the stapes internaUy. 

 It presents for examination a bodv and two processes. The body is deeply excavated anteriorly 

 for the reception of the head of the malleus. The short process projects backward, and is 

 connected bv means of ligamentous fibres to the posterior wall of the tympanum, near the 

 entrance to the mastoid antrum. The long process is slender, and directed downward and in- 

 ward, and lies parallel with the manubrium of the malleus. On the medial aspect of the distal 

 extremity of this process is the lenticular process (orbicular tubercle), separate in early life, but 



