536 ORGANS OF THE SENSES. 



The suspensory ligament of the malleus is a delicate, round bundle of fibres, 

 which descends perpendicularly from the roof of the tympanum to the head of the 

 malleus. 



The posterior ligament of the incus is a short, thick, ligamentous band, which 

 connects the extremity of the short process of the incus to the posterior wall of 

 the tympanum, near the margin of the opening of the mastoid cells. 



The annular ligament of the stapes connects the circumference of the base of 

 this bone to the margin of the fenestra ovalis. 



A suspensory ligament of the incus has been described by Arnold, descending 

 from the roof of the tympanum to the upper part of the incus, near its articulation 

 with the malleus. 



The Muscles of the tympanum are three : 



Tensor tympani. Laxator tympani. Stapedius. 



The Tensor tympani, the largest, is contained in a bony canal, above the osseous 

 portion of the Eustachian tube, from which it is separated by the processus 

 cochleariformis. It arises from the under surface of the petrous bone, from the 

 cartilaginous portion of the Eustachian tube, and from the osseous canal in which 

 it is contained. Passing backwards, it terminates in a slender tendon, which is 

 reflected outwards over the processus cochleariformis, and is inserted into the 

 handle of the malleus, near its root. It is supplied by a branch from the otio 

 ganglion. 



The Laxator tympani major (Sommering) arises from the spinous process of 

 the sphenoid bone, and from the cartilaginous portion of the Eustachian tube; 

 passing backwards through the Glaserian fissure, it is inserted into the neck of 

 the malleus, just above the processus gracilis. It is supplied by the tympanic 

 branch of the facial. 



The Laxator tympani minor (Sommering) arises from the upper and back part 

 of the external meatus, passing forwards and inwards between the middle and 

 inner layers of the membrana tympani; it is inserted into the handle of the 

 malleus, and processus brevis. This is considered as a ligament by some 

 anatomists. 



The Stapedius arises from the sides of a conical cavity hollowed out of the 

 interior of the pyramid ; its tendon emerges from the orifice at its apex, and, 

 passing forwards, is inserted into the neck of the stapes. Its surface is aponeurotic, 

 its interior fleshy, and its tendon occasionally contains a slender bony spine, 

 which is constant in some mammalia. It is supplied by a filament from the facial 

 nerve. 



Actions. The Tensor tympani draws the membrana tympani inwards, and thus 

 heightens its tension. The Laxator tympani draws the malleus outwards, and 

 thus the tympanic membrane, especially at its fore part, is relaxed. The Stapedius 

 depresses the back part of the base of the stapes, and raises its fore part. It 

 probably compresses the contents of the vestibule. 



The Mucous Membrane of the tympanum is thin, vascular, and continuous with 

 the mucous membrane of the pharynx, through the Eustachian tube. It invests 

 the ossicula, and the muscles and nerves contained in the tympanic cavity, forms 

 the internal layer of the membrana tympani, covers the foramen rotundum, and 

 is reflected into the mastoid cells, which it lines throughout. In the tympanum 

 and mastoid cells, this membrane is pale, thin, slightly vascular, and covered with 

 ciliated epithelium. In the osseous portion of the Eustachian tube, the membrane 

 is thin; but in the cartilaginous portion it is very thick, highly vascular, 

 covered with laminar ciliated epithelium, and provided with numerous mucous 

 glands. 



The Arteries supplying the tympanum are five in number, viz., the tympanic 

 branch of the internal maxillary, which supplies the membran/i tympani ; the 

 stylo-mastoid branch of the posterior auricular, which supplies the back part of 

 the tympanum and mastoid cells ; the smaller branches being the petrosal branch 



