888 



THE NERVOUS SYSTEM 



scends from its central part which is elevated, and consequently it forms a tent-shaped 

 covering. Its upper surface is in relation with the tentorial surfacesof the hemispheres, 

 and its lower surface conforms accurately to the upper 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 posterior 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 protuberance 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 



FIG. 060. THE CRANIUM WITH ENCEPHALON REMOVED TO SHOW THE FALX CEREBRI, THE 

 TENTORIUM CEKEBELLI, AND THE PLACES WHERE THE CRANIAL NEKVES PIERCE THE DURA 

 MATER. (Sappey.) 



roriiTH XF.RVE Tinr.ii XEHVI-: 



Fall cerebri 



X WO Mi XKRVE 



Tentorium 

 cerebellt 



Transverse 

 sinus 



petrosal sinus 

 Fall cere belli 



SEVENTH AND 

 EIGHTH 

 NERVES 



NINTH, TENTH, ANT> 

 ELEVENTH NER VES 



TWELFTH NERVE 



SECOND CERVICAL NERVE 



Ligamentum dentieulatum 



FIFTH 

 NER VE 



FIRST 



CERVICAL 



NERVE Inferior petrosal sinus 



the anterior clinoid processes. A depressed angle is formed between the inner and 

 outer borders of the tentorium in the middle fossa of the skull at the outer side of the 

 posterior clinoid process, and in this angle the root of the third nerve pierces the 

 inner layer of the dura mater. 



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

 wards and forwards, into the small groove (posterinr ccrebdlar notch), between the 

 hemispheres of the cerebellum. Its base is attached to the tentorium: its superior 

 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 behind 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 sellae is a small circular fold, deficient in the centre, which 

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

 outer border is attached to the clinoid processes and the limbus of the sphenoid, 



