154^ 



A MANUAL OP ANATOMY 



nerve) of the pneumogastric, and {3) branches from the tympanic 

 plexus. 



Secondary Membrane of the Tympanum.— -This membrane closes 

 the fenestra rotunda on the inner wall of the tympanum, and sepa- 

 rates the tympanic cavity from the scala tympani of the cochlea. 

 It is concave towards the tympanum, and, like the membrana 

 tympani, it consists of three layers. The external layer is formed by 

 the tympanic mucous membrane ; the middle layer is fibrous ; and 

 the internal layer is formed by the lining membrane of the cochlea. 



The mastoid antrum and mastoid air-cells will be found described 

 in connection with the temporal bone, and a description of the 

 Eustachian tube will be found on p. 1274. 



Facet for Incus 



Short Process 



Long Process,. 



Handle -•-'' 



Fig, 646. — The Malleus. 

 I, Anterior View ; 2, Posterior View. 



r; _^. Ossicles of the Tympanum. 



The tympanum contains three small bones, arranged in the form 

 of a chain which extends from the membrana tympani to the fenestra 

 ovalis. The bones are the malleus, the incus, and the stapes. 



The malleus is related to the 

 membrana tympani, the stapes 

 to the fenestra ovalis, and the 

 incus occupies an intermediate 

 position between these two. 



The malleus is so named from 

 its resemblance to a hammer. 

 It is composed of a head, neck, 

 handle, and two processes, 

 namely, long and short. The 

 head is the upper, enlarged, 

 rounded end. Posteriorly it pre- 

 sents a saddle-shaped facet, 

 directed obliquely downwards and inwards, for articulation with the 

 incus in a synovial joint. The neck is the constricted part below the 

 head. The handle (manubrium) is directed downwards, inwards, and 

 backwards from the neck ; it is compressed from before backwards, 

 and slightly curved, and it terminates in a slight knob. It lies between 

 the fibrous and mucous layers of the membrana tympani, descending, 

 to a point a little below the centre of the membrane. It is firmly 

 attached to the fibrous layer by its periosteum. The tensor tym- 

 pani muscle is inserted into its inner part, close to its root. The 

 long process (processus gracilis), which is slender, springs from the 

 front of the neck, and is directed forwards and downwards to the 

 fissure of Glaser, where it is embedded in fibres which form part of 

 the anterior ligament of the malleus, and connect it to the margins 

 of the fissure. The long process is in the adult for the most part 

 replaced by fibrous tissue, except close to the neck of the malleus. 

 In early life it is continuous with Meckel's cartilage. The short 

 process (processus brevis) is situated immediately below the long 

 process. It is directed outwards to the upper part of the membrana 



