128 PRACTICAL ANATOMY. 



arachnoid. Remove this with one braimvard sweep of the forceps, and expose 

 the optic chiasm. Behind this see the infundibulum, attached above to the brain 

 and below to the pituitary body. See it passing through a hole in the dia- 

 phragma sellae. 



The internal carotid artery will be seen to the outer side of the optic nerve. 

 Do not call this large artery the ophthalmic. Cut the optics behind the chiasm. 

 Cut the internal carotid artery close to the anterior clinoid process. You will 

 now expose the third nerve by breaking the prolongation of arachnoid about it. 



The fourth cranial nerve lies under the free margin of the tentorium. You 

 will see the tentorium attached to the superior border of the petrosa in front. 

 Cut along this border on both sides. Now gently retract the brain. The fourth 

 nerve will pass to the outer side of the posterior clinoid process and disappear 

 under the dura into the cavernous sinus. 



The fifth nerve will now be seen crossing the superior border of the petrosa, 

 near the apex. It also disappears under the dura through the trigeminal 

 notch. 



The sixth nerve will be seen going through the dura one inch below the 

 dorsum sellae. It passes beneath the dura to gain the cavernous sinus with the 

 third and fourth nerves, and the ophthalmic branch of the fifth nerve. 



Find now the seventh or facial nerve, the eighth or auditory nerve, 

 and the auditory artery passing through the internal auditory meatus on the 

 posterior surface of the petrosa. Note the funnel of arachnoid that accompanies 

 these structures to the foramen. The ninth, tenth, and eleventh nerves will 

 now be seen leaving the cranial cavity through the jugular foramen. The 

 twelfth nerve leaves as two twigs : after passing through the dura they unite 

 as one nerve, and leave the skull by the anterior condyloid foramen. 



FORAMINA AT THE BASE OF THE SKULL AND THE STRUCTURES THEY TRANSMIT. 



Foramen Caecum Transmits an emissary vein. 



Nasal Slit Transmits the nasal branch of the ophthalmic 



nerve. 



Olfactory Foramina Twenty in number, transmit the olfactory nerves. 



Optic Foramina, ...... Transmit the optic nerves and the ophthalmic 



artery. 



Sphenoidal Fissure Transmits third, fourth, sixth, and first divisions of 



the fifth nerve, the ophthalmic vein, and sym- 

 pathetic nerves. 



Foramen Rotundum, .... Transmits the second or superior maxillary divi- 

 sion of the fifth nerve. 



Foramen Ovale, ...... Transmits the third division of fifth nerve and 



small meningeal artery. 



Foramen Spinosum, Transmits the great or middle meningeal artery. 



Foramen, Sphenotic Transmits internal carotid and the facial and 



carotid petrosals for Vidian nerve. 



Hiatus Fallopii Transmits petrosal branch of the Vidian nerve. 



Petrosal Foramen Transmits the smaller petrosal nerve. 



Carotid Canal Transmits internal carotid artery and sympathetic 



nerves. 



Internal Auditory Meatus, . . Transmits seventh and eighth nerves and auditory 



artery. 



Jugular Foramen Transmits jugular vein, ninth, tenth, and eleventh 



nerves. 



Anterior Condyloid Foramen, Transmits the hypo-glossal nerve the twelfth 



nerve. 



Foramen Magnum, Transmits (i) spinal cord and its meninges; (2) 



the vertebral arteries and their sympathetic 

 nerves ; (3) the spinal accessory nerve the 

 eleventh nerve. Note the eleventh nerve 

 coming up through the foramen, passing for- 

 ward, and leaving the cranium with the ninth 

 and tenth nerves by the jugular foramen. 



