.J74 ANATOMY IN A NUTSHELL 



of the tympanum and is formed by the following nerves: (1) Jacob-son's 

 nerve, (2) great superficial petrosal nerve, (3) small superficial petrosal nerve, 

 I I small deep petrosal. 



The middle ear or tympanum is filled with air and contains the malleus, 

 incus and stapes. These form a chain of bones which transmits the impulses of 

 sound waves between the tympanic membrane and the parilymphand endo- 

 lymph of the internal ear. 



The malleus (hammer) consists of the following parts, (1) a head, (2) a neck, 

 (3) :i shorl process, (4) long process (process gracilis) (5) handle (manubrim). 

 The handle is connected with the middle layer of the drum head and is situated 

 between this middle and mucous layer. The short process (process brevis) 

 is attached to the Tensor tympani muscle. The long process is received into 

 the Glaseriarj fissure. The head, which is situated in the attic, is connected 

 with the roof of the attic by the superior ligament of the malleus and it articu- 

 lates with the body of the incus. 



The Incus (anvil) has the following parts, (1) a body (head), (2) a long 

 process, (3) a short process. The body articulates with the head of the malleus. 

 This joint is covered by a capsular ligament and lined by synovial membrane. 

 'I Tie shorl process articulates with the fossa incudis in the attic to which it is 

 connected by fibrous tissue. The long process articulates with the head of the 

 -tapes. The end of this process is called os orbiculare. This os orbiculare is 

 the smallest bone in the body. In adult life it forms part of the incus. 



The stapes (stirrup) has the following parts, (1) a head, (2) a neck, (3) a 

 base (foot piece), (4) two crura (branches). The head articulates with the os 

 orbiculare of the incus. This is a ball-and-socket joint. 



The base fits on the membrane closing the fenestra ovalis. The neck re- 

 ceives the tendon of the Stapedius. 



The Ligaments of the malleus, incus, and stapes are five besides the capsular 

 ligaments of their articulations. 



1. The superior ligament of the MALLEUsisa fibrous band passing from 

 the head of the malleus to the outer part of the roof of the attic. 



•_'. Tin: interior ligament of the malleus is attached to the anterior 

 wall of the tympanum and to the anterior part of the head and neck of the 

 malleus. It is sometimes described as the Laxator tympani muscle. 



:;. Tiii': external ligament of the malleus is attached to the neck of 

 the malleus by its apex and to the margin of notch of Rivini by its base. 



1. The [NTERNAL ligament of the malleus extends from the tip of the 

 processus cochleariformis to the insertion of the Tensor tympani tendon. 



5. The ligament of the incus is attached to the short process of the 

 incus and to the posterior wall of the attic near the orifice of the mastoid ant urn. 



Besides these five ligaments just named we have capsular ligaments around 

 the joints between the malleus and incus, and between the incus and stapes. 



The muscles of the tympanum have been described on page 523. 



The mastoid antrum is situated posterior to the tympanum and is lined 

 with mucous membrane. It opens in the attic of the tympanum and into the 

 mastoid cells. 



