Fracture of Skull 13 



In certain cases in which the Eustachian tube has been blocked, 

 the surgeon has endeavoured to ventilate the rmddle ear by making a 

 permanent drill-opening into the mastoid cells, but the proceeding is 

 dangerous, meningitis being apt to follow. 



The mastoid foramen transmits- a large vein into the lateral sinus, 

 and a branch of the occipital artery for the dura mater ; and in acute 

 otitis, when every neighbouring vessel is engorged with blood, the 

 application of a few leeches behind the ear affords direct and imme-' 

 diate relief. 



If matter be long pent up in the mastoid cells it may find its escape 

 into the cranial cavity and set up a purulent and fatal meningitis. 

 Moreover, the lateral sinus, which is close upon the inner side of 

 the cells, may become inflamed in the course of otitis media, and, 

 septic coagulation of its contents taking place, pyaemia ensues. 



On the inner aspect of the mastoid process is a fossa for the origin 

 of the posterior belly of the digastric, and, more internally still, is the 

 groove for the occipital artery. 



On the cerebral surface of the mastoid portion is the wide and 

 shallow groove for the lateral sinus (p. 39), into which the mastoid 

 vein is opening. When the question arises of trephining in the region 

 of the mastoid cells the surgeon must remember that the lateral sinus 

 specially grooves the front of the cranial aspect of the mastoid pro- 

 cess (Tillaux). 



The petrous portion, hard as a stone (Tre'rpos), is wedged forwards 

 and inwards into the floor of the skull. Its base is between the 

 squamous and mastoid portions, and receives the external auditory 

 meatus, which is surrounded by . the outgrowth of the horse-shoe 

 auditory process, to the surface of which the cartilage of the pinna 

 is attached. Through the petrous portion winds the canal for the 

 internal carotid artery (p. 33) ; by the articulation with the occipital 

 the jugular foramen is enclosed. 



The internal and middle ear are also contained within the petrous 

 bone, and the facial nerve winds through it from the internal auditory 

 meatus to its exit from the aqueductus Fallopii at the stylo-mastoid 

 foramen. 



Fracture across this brittle bone may be followed by rupture of the 

 large vein and artery, and of the membrana tympani, and, further, 

 by bleeding from the ear. The perilymph may also escape from the 

 internal ear, diluting the blood, or staining the pillow long after 

 bleeding has ceased. The facial nerve having been torn across, 

 paralysis of the muscles of expression ensues. 



On the anterior surface of the petrous bone is the upheaval which 

 is caused by the superior semicircular canal of the internal ear ; just 

 outside this is the thin plate of bone roofing in the middle ear. Nearer 

 to the middle line is the hiatus Fallopii, by which the petrosal branch of 

 the facial escapes from the aqueduct to join the Vidian nerve. 



