THE MIDDLE EAR 719 



cartilage of the Eustachian tube is intermediate between hyaline and 

 elastic cartilage. 



The circumflexus, or tensor palati muscle, which has already been 

 described in connection with deglutition, is attached to the anterior 

 margin, or the hook of the cartilage. The attachments of this muscle 

 have been accurately described by Riidinger, who called it the dilator 

 of the tube. 



The action of certain of the muscles of deglutition dilates the pharyn- 

 geal opening of the Eustachian tube. If the mouth and nostrils are 

 closed and several repeated acts of deglutition are made, air is drawn 

 from the tympanic cavity, and the atmospheric pressure renders the 

 membrane of the tympanum tense, increasing its concavity. By one or 

 two lateral movements of the jaws, the tube is opened, the pressure of 

 air is equalized and the ear returns to its former condition. The nerves 

 animating the dilator tubae come from the pneumogastric and are derived 

 originally from the spinal accessory. 



A smooth mucous membrane forms a continuous lining for the 

 Eustachian tube, the cavity of the tympanum and the mastoid cells. 

 In all parts it is closely adherent to the subjacent tissues, and in the 

 cavity of the tympanum it is very thin. In the cartilaginous portion 

 of the Eustachian tube there are mucous glands, which are most abun- 

 dant near the pharyngeal orifice, and gradually diminish in number 

 toward the osseous portion, in which there are no glands. Throughout 

 the tube the surface of the mucous membrane is covered with conoidal 

 cells of ciliated epithelium. The mucous membrane of the tympanic 

 cavity is very thin, consisting of little more than epithelium and a layer 

 of connective tissue. It lines the walls of the cavity and the inner sur- 

 face of the membrana tympani, is prolonged into the mastoid cells and 

 covers the ossicles and those portions of the muscles and tendons which 

 pass through the tympanum. On the floor of the tympanic cavity and 

 on its anterior, inner and posterior walls, the epithelium is of the co- 

 noidal ciliated variety. On the promontory, roof, ossicles and muscles, 

 the cells are of the pavement-variety and not ciliated, the transition from 

 one form to the other being gradual. The entire mucous membrane 

 contains lymphatics, a plexus of nerve-fibres and nerve-cells, with some 

 peculiar cells, the physiology of which is not understood. 



The above is merely a general sketch of the physiological anatomy 

 of the middle ear, and it will not be necessary to treat more fully of the 

 cavity of the tympanum, the mastoid cells or the Eustachian tube, except 

 as regards certain points in their physiology. The minute anatomy of 

 the membrana tympani and the articulations of the ossicles can be more 

 conveniently considered in connection with the physiology of these parts. 



