920 THE ORGANS OF SENSE. 



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 two : 



Tensor tympani. Stapedius. 



The Tensor tympani, the larger, is contained in the 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 backward through the canal, it terminates in a slender 

 tendon which enters the tympanum and makes a sharp bend outward round the 

 extremity of 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 iStapedius arises from the side of a conical cavity hollowed out of the inte- 

 rior of the pyramid; its tendon emerges from the orifice at the apex of the pyra- 

 mid, and, passing forward, 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 the tympanic 

 branch of the facial nerve. 



Actions. The Tensor tympani draws the membrana tympani inward and thus 

 heightens its tension. The Stapedius draws the head of the stapes backward, and 

 thus causes the base of the bone to rotate on a vertical axis drawn through its own 

 centre : in doing this the back part of the base would be pressed inward toward 

 the vestibule, while the fore part would be drawn from it. It probably compresses 

 the contents of the vestibule. 



The mucous membrane of the tympanum is thin, slightly 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 six in number. Three of them are 

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

 supplies the membrana tympani ; the Vidian 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, 

 which enters through the hiatus Fallopii ; a branch from the ascending pharyngeal, 

 and another from the Vidian which pass up the Eustachian tube ; and the tympanic 

 branch from the internal carotid, given off in the carotid canal and perforating the 

 thin anterior wall of the tympanum. 



The veins of the tympanum terminate in the temporo-maxillary vein and in 

 the superior petrosal sinus. 



The nerves of the tympanum may be divided into 1, those supplying the 

 muscles ; 2, those distributed to the lining membrane ; 3, branches communicating 

 with other nerves. 



Nerves to Muscles. The Tensor tympani is supplied by a branch from the otic 

 ganglion ; the Stapedius, by the tympanic branch of the facial (Sbmmerring). 



The nerves distributed to the lining membrane are derived from the tympanic 

 plexus. 



The communications which take place in the tympanum are between the 

 tympanic branch of the glosso-pharyngeal with the sympathetic and with filaments 

 derived from the intumescentia ganglioformis of the facial. 



The tympanic branch of the glosso-pharyngeal (Jacobson's nerve) enters the 



