588 THE CRANIAL NERVES. 



in distinct foramina of the cranium, others are grouped together in one 

 foramen. The numerous small olfactory nerves descend into the nose 

 through the cribriform plate of the ethmoid bone ; the optic nerve pierces 

 the root of the lesser wing of the sphenoid bone ; the third, fourth, and 

 sixth nerves, with the ophthalmic division of the fifth nerve, pass through the 



Fig. 399. 



Fig. 399. INTERNAL VIEW OF THE B/SE OF THE SKULL, SHOWING THE PLACES OF EXIT OF 

 THE CKANIAL NERVES. 



The dura mater is left in great part within the base of the skull ; the tentoriuin is 

 removed and the venous sinuses are opened. Ou 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 fissure. 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 the left side opposite to the middle of the three divisions of the trigeminus, 

 which, together with the ganglion and greater 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 oppo- 

 site 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 hypoglossal nerve as it passes through the anterior 

 condyloid foramen. On the left side at 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 artery. The explanation of the 

 remaining references in this figure will be found at p. 461. 



