702 ORGANS OF SENSE. 



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 articu- 

 lation 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 

 osseus portion of the Eustachian tube, from which it is separated by the pro- 

 cessus 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 otic ganglion. 



The Laxator Tympani Major (Sommerring) arises from the spinous process 

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

 tube, and passing backwards through the Glaserian fissure, 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 (Sommerring) arises from the upper and back 

 part of the external meatus, passes forwards and inwards between the middle 

 and inner layers of the membrana tympani, and is inserted into the handle of 

 the malleus, and processus brevis. This is regarded 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 the apex of the 

 pyramid, and passing forwards, is inserted into the neck of the stapes. Its sur- 

 face 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 tenison. 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 rotun- 

 dum ; 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. Two of them are 

 larger than the rest, viz., the tympanic branch of the internal maxillary, which 

 supplies the membrana tympani ; and the stylo-mastoid branch of the posterior 

 auricular, which supplies the back part of the tympanum and mastoid cells. 

 The smaller branches are, the petrosal branch of the middle meningeal, and 

 branches from the ascending pharyngeal and internal carotid. 



The veins of the tympanum terminate in the middle meningeal and pharyngeal 

 veins, and, through these, in the internal jugular. 



The nerves of the tympanum may be divided into: 1. Those supplying the 

 muscles; 2. Those distributed to the lining membrane; 3. Branches communi- 

 cating with other nerves. 



