IS 



APPLIED ANATOMY. 



parietal bone. It sends branches forward to the frontal region and backward to the 

 parietal and temporal regions. During two to three centimetres of its course, at the 

 pterion, it passes entirely through bone, and therefore if a fracture occurs at this 

 point it must of necessity tear the artery. The posterior branches are not regular in 

 their course, one passing backward, low down, parallel to the zygoma, and another 

 higher up in the direction of the parietal eminence. The branches of the meningeal 

 artery nourish the bone as well as the dura, therefore if the dura is loosened from 

 the bone hemorrhage from these branches occurs. The most frequent site of middle 

 meningeal hemorrhage is in the region of the pterion or temple. 



In trephining for it, the centre of the trephine is to be placed on an average of 

 4 cm. (1^2 ln - ) behind the external angular process of the frontal bone, and on a 

 level with the upper edge of the orbit or 4.5 cm. (i^ in.) above the zygoma. If 

 the artery is not sufficiently exposed more bone is to be removed by the rongeur 



olfactory 



and optic 



4th trochlear (pathetic) 



5th trigeininal (trifacial) 

 6th abducent 



7 th-facial 



8th auditory 

 , 9th glossopharyngeal 

 . loth vagus (pneumojjastrlc) 

 . nth spinal accessory 



i2th hypoglossal 



FIG. 25. Exit of cranial nerves at the base of the skull. 



forceps. It is in this region that epidural hemorrhages are apt to be extensive, 

 because the vessels torn are the largest; but epidural hemorrhage can also occur in 

 the frontal region from the anterior branches and in the parietal from the posterior. 



Trephining for bleeding from the posterior branch of the middle meningeal 

 artery is somewhat uncertain. In some cases the artery runs low down, about 2 cm. 

 (4/5 in.) above the zygoma and parallel to it. In other cases it runs upward and 

 backward toward the parietal eminence. The trephine may be placed as high up 

 as for the anterior branch of the middle meningeal artery, 4.5 cm. (i^ in.), and 

 5 cm. (2 in. ) farther back. This will be below and anterior to the parietal eminence 

 and about midway on a line joining the parietal eminence and external auditory 

 meatus. After the button of bone has been removed, additional bone may be cut 

 away with the rongeur forceps until access can be had to the bleeding point (see 

 page 23 for a case of rupture without fracture). 



Rupture of the large venous sinuses and of the small vessels passing between the 

 bone and dura also contribute to the formation of the clot. Owing to the firmer 



