THE DURA MATER 



915 



tent-shaped covering. Its superior surface is in relation with the tentorial surfaces 

 of the hemispheres, and its inferior surface conforms accurately to the superior 

 surface of the cerebellum. The outer or convex border of the fold is attached 

 on each side to the posterior clinoid process, the superior border of the petrous 

 portion of the temporal bone, the mastoid portion of the temporal bone, the pos- 

 terior inferior angle of the parietal bone, and the horizontal ridge of the occipital 

 bone. The transverse sinus lies in this border. From the internal occipital pro- 

 tuberance to the mastoid portion of the temporal bone and along the petrous part 

 of the temporal bone it encloses the superior petrosal sinus. 



The greater part of the inner or anterior border of the tentorium is free, and it 

 forms the superior and lateral boundaries of an arched cavity, the tentorial notch 

 or foramen ovale of Pacchioni, which encloses the mesencephalon, and through 

 which ascend the cerebral peduncles and the posterior cerebral arteries. The 

 anterior extremities of the inner border cross the outer border, and they are 

 attached to the anterior clinoid processes. A depressed angle is formed between 



Fig. 721. — Showing the Upper Surface of the Tentorium Cerebelli and the Tentoriai, 

 Notch through which the Mid-brain and Posterior Cerebral Arteries enter the 

 Middle Fossa of the Cranium. 



Infundibulum 



Internal carotid 



artery 



Optic tract 

 Oculomotor nerve 

 Cerebral 

 peduncle 

 Aqueduct of 

 cerebrum 

 Mesencephalon 



Falx cerebri 



Tentorium cere- 

 belli 



Straight sinus 



Crista galli 



Optic nerve 



Spheno-parietal 

 sinus 



Middle cerebral 



artery 

 Arterior cerebral 



artery 

 Posterior commu- 

 nicating artery 

 Cavernous sinus 

 Superior cerebel- 

 lar artery 

 Posterior cerebral 



artery 

 Superior petrosal 



sinus 

 Free border of 

 tentorium bound- 

 ing tentorial notch 



Transverse sinus 



Superior sagittal sinus 



the inner and outer borders of the tentorium in the middle fossa of the skull at 

 the lateral portion of the posterior clinoid process, and in this angle the root of the 

 oculo-motor nerve pierces the inner layer of the dura mater. 



The falx cerebelli is a small, sickle-shaped, triangular fold which projects 

 forward into the small groove {'posterior cerebellar notch), between the hemispheres 

 of the cerebellum. Its base is attached to the tentorium; its postero-inferior 

 border, along which runs the occipital sinus, is attached to the internal occipital 

 crest. Its anterior border is free, and its apex, which lies immediately above the 

 foramen magnum, usually bifurcates as it disappears anteriorly, grasping the 

 foramen magnum from behind. Bifurcation is always the case when the internal 

 occipital crest splits below to enclose a vermiform fossa. 



The diaphragma sellse is a small circular fold, deficient in the centre, which 

 projects horizontally from the margins of the hypophyseal fossa or sella turcica. 

 Its lateral border is attached to the clinoid processes and the limbus of the sphe- 



