448 Anatomy Applied to Medicine and Sutgety. 



num to the brain. In children, under one year of age, 

 there is a suture present in the layer of bone that forms 

 the roof the petro-squamosal suture. The existence of 

 this suture still further adds to the possibility of cerebral 

 infection developing from disease of the middle ear. The 

 anterior wall of the tympanum has in front of its lower 

 portion, the carotid canal ; and in this situation the Eu- 

 stachian tube opens into the cavity from the pharynx. The 

 opening of this Eustachian tube is about one-sixth of an 

 inch above the floor of the cavity, so that, fluids finding 

 entrance into the tympanum through this tube might re- 

 main in it, and induce inflammatory action ; and further, the 

 fact of the opening being above the lower level would in- 

 terfere with proper drainage when pus is present in the 

 middle ear. The floor of the tympanum separates this 

 cavity from the jugular fossa, so that, in fractures of this 

 portion of the tympanic wall, the jugular vein might be 

 wounded, just as in fractures of the anterior wall the car- 

 otid artery could be injured. The posterior wall presents 

 the openings that lead into the mastoid antrum and cells. 

 The cavity contains the ossicles, or small bones, which 

 convey the vibrations of the membrane, that have been set 

 up by the sound waves, to the perilymph and endolymph 

 of the internal ear. The chorda tympani nerve passes, 

 from behind forwards, through the tympanum, while the 

 facial nerve is contained in a canal in the upper part of its 

 inner wall. Behind the tympanum is the antrum of the 

 mastoid, which is present at birth, and, in the adult, is 

 about the size of a pea. The antrum is separated by a 

 thin plate of bone from the cranial cavity and communi- 

 cates with the mastoid cells. 



Otitis Media. Disease of the middle ear may spread 

 to the cerebral sinuses through the venous channels, above 

 mentioned, in the roof of the tympanum, or, in the infant, 



