chap, ii.j BONY VAULT OF THE CRANIUM. 27 



through a rupture in the tympanic membrane, and ia 

 derived from the vessels of the tympanum and its 

 membrane, or from an intracranial extravasation, and 

 in some cases from a rupture of one of the sinuses 

 about the petrous bone. The blood may follow the 

 Eustachian tube, and may escape from the nose or 

 mouth, or be swallowed and subsequently vomited. 

 To allow of the escape of cerebro-spinal fluid by the 

 ear (" the serous discharge "), (A) the fracture must 

 have passed across the internal auditory meatus ; (B) 

 the tubular prolongation of the membranes in that 

 meatus must have been torn; (c) there must be a com- 

 munication between the internal ear and the tympa- 

 num ; and (D) the membrana tympana must have been 

 lacerated. (3) In fractures of the posterior fossa an 

 extravasation of blood may appear about the mastoid 

 process or at the nape of the neck, or may even 

 extend into the cervical region. 



It may be added that in compound fractures of the 

 vault associated with tearing of the dura mater and 

 arachnoid, an escape of cerebro-spinal fluid has in a 

 few rare instances been noted. After simple fracture 

 of the vault in children a swelling may form at the 

 injured part, which fluctuates, becomes tenser when 

 the patient cries, and may possibly pulsate synchro- 

 nously with the brain. Such swellings are due to a 

 collection of cerebro-spinal fluid beneath the scalp, and 

 indicate a coincident rupture of the brain membranes. 

 In cases of free serous discharge from the ear after 

 injury to the head, but without fracture, the fluid is 

 derived from the mastoid cells, and escapes through a 

 rupture in the tympanic membrane. In a few instances 

 it may possibly be blood serum, or depend upon mild 

 catarrh of the meatus. Some authors assert that it 

 may be due to the escape of the liquor Ootunnii, but 

 the very minute quantity of that fluid in the ear 

 renders the suggestion improbable. 



