108 CLINICAL APPLIED ANATOMY. 



When the injury to the optic nerve is primary, that is to say 

 when it is torn coincidently with the fracture of the bone, the 

 loss of vision is usually permanent, but when the amblyopia is 

 due to pressure on the nerve filaments by inflammatory exudation 

 or callus, it may be only transitory. 



In the middle fossa the following cranial nerves may be in- 

 volved the third, the fourth, the fifth and the sixth. Inter- 

 ference with the third, fourth and sixth gives rise to squint, 

 and that of the fifth causes failure of movement of the muscles 

 of mastication and loss of sensation in the skin of the whole of 

 the face, except that area supplied by the great auricular over 

 the parotid gland. 



When the posterior fossa is involved, particularly where the 

 fracture runs across the petrous portion of the temporal bone and 

 involves the tympanic cavity, blood and cerebro-spinal fluid escape 

 from the external auditory meatus. The nerves that may be 

 injured are the seventh, the eighth, the ninth, the tenth, the 

 eleventh and the twelfth. 



Facial paralysis as the outcome of primary injury to the 

 seventh nerve whilst it is passing through the aqueduct is common 

 in fractures involving the petrous bone. Loss of function of the 

 nerve may again be due to secondary inflammation. 



Injury to the eighth nerve may induce loss of hearing. 



In the case of the nerves passing through the posterior lacera- 

 ted foramen the damage so usually implicates the tenth that 

 sudden death may result. 



The hypoglossal nerve, when torn or pressed upon by fractures 

 running through the anterior condyloid foramen, is deprived of 

 function, and impairment of action, or paralysis, of the muscles 

 of the tongue ensues. 



FRACTURES OF KIBS. 



Kibs are exposed to violence in one of two ways, either by 

 a direct blow, when the bone will break at the spot to which 

 the violence is applied, or by pressure from before backwards 



