REMOVAL OF THE BRAIN 215 



nerve may be distinguished. At a higher level on each side 

 the two rootlets of the hypoglossal nerve pierce the dura, as 

 they pass into the hypoglossal canal (O.T. anterior condyloid 

 foramen). The spinal root of the accessory nerve passes 

 through the foramen magnum into the cranium, posterior to 

 the ligamentum denticulatum, and, turning laterally over 

 the margin of the foramen magnum, it joins the cerebral 

 fibres of the accessory and the tenth nerve, with which it 

 passes through an aperture in the dura opposite the jugular 

 foramen. Immediately above the eleventh and tenth nerves 

 the smaller trunk of the ninth nerve pierces the dura. Above 

 the ninth nerve the eighth nerve and the motor and sensory 

 roots of the seventh nerve pass into the internal acustic 

 meatus, accompanied by the small auditory branch of the 

 basilar artery and the auditory vein. The two roots of the 

 seventh nerve lie in a groove on the upper and anterior 

 aspect of the eighth, the small sensory root (O.T. pars 

 intermedia) being situated between the motor root and the 

 eighth nerve. The small motor and the large sensory root 

 of the fifth nerve pass through an opening in the dura which 

 lies above and medial to the internal acustic meatus ; and the 

 sixth nerve pierces the dura mater below and to the medial 

 side of the opening for the fifth nerve, opposite the side of 

 the base of the dorsum sellae. The small fourth nerve 

 pierces the under surface of the free border of the tentorium 

 at the point where it is crossing the attached border. 



After the dissectors have familiarised themselves with the 

 positions of the cerebral nerves as they pierce the dura mater, 

 they should examine the falx cerebelli and complete the 

 display of the cranial blood sinuses. 



The Falx Cerebelli is a small sagittal fold of the inner 

 layer of the dura mater which projects anteriorly, between the 

 lateral lobes of the cerebellum, from the internal occipital 

 crest (Figs. 87, 89). 



Sinus Transversus (O.T. Lateral). The horizontal part of 

 the transverse sinus has already been traced from the internal 

 occipital protuberance to the superior border of the petrous 

 part of the temporal bone, where it turns downwards to 

 the jugular foramen. At first the descending portion runs 

 downwards, on the inner surface of the mastoid part of the 

 temporal bone, and then anteriorly and again downwards 

 across the upper and anterior surfaces of the jugular process 



II 14 c 



