20 SURGICAL ANATOMY OF THE CRANIUM. 



bones, and in the occipital region the ribs of the occipi- 

 tal bone itself. 



In almost all cases, when the cranium is struck, the 

 parietal region is the seat of the injury ; the bone is 

 fractured at the spot, and the line of fracture runs 

 through the temporal bone, which, from the fact of its 

 containing so many cavities and foramina, its texture, 

 and the inclination of the axis of the petrous portion, 

 readily gives way. A fracture of the base may also 

 occur from a fall on the feet or on the buttock, the force 

 being transmitted along the spinal column, and meeting 

 the skull at the condyles. Rupture of the brain-sub- 

 stance, however, is common by contre-coup. The course 

 of such fractures of the base may be anatomically deter- 

 mined by the effects produced upon the nerves issuing 

 from the skull, the most frequent being facial paralysis 

 from lesion of the portio dura whilst in the aqueductus 

 Fallopii. 



Fractures of the base of the cranium are generally 

 associated with ecchymosis of the eyelids and effusion 

 of blood from the external auditory meatus. The exist- 

 ence of subconjunctival ecchymosis is of great impor- 

 tance in the diagnosis of this injury ; the escaped blood 

 infiltrates the cellular tissue of the orbit, passes through 

 the openings in the capsule of Tenon, and so gets into 

 the subconjunctival cellular tissue (vide Orbital Region). 



The surgical anatomy of the temporal bone presents 

 considerable additional points of practical importance, 

 as it contains the organ of hearing and the parts acces- 

 sory to it. 



The external auditory canal has a direction inwards 

 and forwards, describing a slight general curve, the con- 

 cavity of which is downwards. The outer third of the 



