522 



THE CRAXIAL NERVES. 



Mode of exit from the cranitim. — Each of the cranial nerves 

 in leaving the cranial cavity passes through a foramen or tubular 

 prolongation of the dura mater : some of these nerves or their main 

 divisions are contamed in distinct foramina of the cranium, others are 



Fig. 330. 



Fig. 330.— Internal A''iew of the Base of the Skull, showing the places of 



E.XIT OF THE CrANIAL NeRVES. (A. T. ) ^ 



The dura mater is left in great part within the base of the skull : the tentorium is 

 I'emoved and the venous sinuses are opened. On the left side a small portion of the roof 

 of the orbit has been removed to show the relation of certain nerves at the cavernous 

 sinus and in the sphenoidal fissiu-e. The roots of the several cranial nerves have been 

 divided at a short distance inside the foramina of the dura mater through which they 

 respectively pass. I, the bulb of the olfactory nerve lying over the cribriform plate of 

 the ethmoid bone ; II, the optic nerves ; that of the left side cut short ; III, placed on 

 the pituitary body, indicates the common oculo-motor nerve : IV, the trochlear nerve ; 

 V, is placed on tlie left side opposite to the middle of the three divisions of the trige- 

 minus, which, together with the ganglion and gi'eater root, have been exposed by 

 opening up the dura mater ; on the right side the greater root is seen ; VI, placed 

 below the foramen of exit of the abducent ocular ; VII, placed on the upper part of the 

 petrous bone opposite the entrance of the facial and auditory nerves into the meatus 

 auditorius internus ; VIII, placed on the petrous bone outside the jugular foramen 

 opposite the place of exit of the three divisions of the eighth pair of nerves ; IX, placed 

 upon the basilar part of the occipital bone in front of the hji^oglossal neiwe as it passes 

 through the anterior condylar foramen. On the left side of the cavernous sinus, the 

 third, fourth, and ophthalmic division of the fifth nerves are seen keeping towards the 

 outer side, while the sixth nerve is deeper and close to the internal carotid arterj'. The 

 explanation of the remaining references in this figure will be found at p. 480. 



