THE CRANIAL DUh'A MATER 



887 



L r li-i enmg. being lined l>y a layer of endot helium ami containing a small amount of the 

 cereoro-.-pinal lymph. 



The subd lira! cavity of t he ha si of I lie hrain is prolonged a short i list an re OUtwardl 

 alon.^ the roots of the various cranial nerve.- before it i.- obliterated by the blending 

 of the dura mater with the sheaths of the nerves. '1 hi- outward extension of t he space 

 is most marked about the opi ic and auditory nerves. In the optic especially, the 

 dura mater remains separate from the nerve throughout ils length, only fusing with 

 its sheath upon the posterior surface of the bulbils oculi (Jig. (' 



( )ne of the most striking dill'erence- between the cranial dura mater and that of 

 the spinal cord is that the inner layer of the former undergoes striking septa-like 

 duplications or folds, forming exceedingly strong partitions which project between 

 the larger subdivi.-ions of the encephalon. These : ,re four in number, two large and 

 two small the falx cerebri and the tentorium cerebelli; the falx cerebelli and the 

 diaphragma selhe. The larger enclose within their folds the great venous sinusi .-. 

 into which most of the spent blood of the encephalon collects to pass outwards by 

 way of the internal jugular veins. 



I in. i I.V.I. CORONAL SECTION OF -IMF. HK.M>, PASSING THKOUQH THE POSTERIOR HORNS OF 



THE I.ATKUA1. \ h\ IKK 



(From a mounted specimen in the Anatomical Department of Trinity College, Dublin.) 



LOffOITUDI- 

 \ II, FASCI- 

 CULI S 



M.i'.tRIXE 

 F1881 /.'/. 



Tratmerte tinut CORPfS DKXT.l TC.V Tentorium oarebelli 



The falx cerebri is the most striking of these partitions. It is a sickle-shaped fold 

 which projects vertically from the vault into the longitudinal fissure between the 

 cerebral hemispheres. It begins attached to the crista galli in front, and arches 

 backwards to terminate by blending with the superior surface of the horizontally 



placed tentorium cerebelli. Its convex, upper border joins the outer layer of the dura 

 alung the medial plum- of the vault, and encloses tiie superior sagittal sinus. Its 

 concave border is free and contains in its posterior two-thirds the smaller inferior 

 sagittal sinus. The anterior and narrower end is often perforated and occasionally 

 so much so as to appear as a Coarse, fibrous reticnlum. The posterior part of the con- 

 cave border touches the upper surface of the coipus callosum. but t he anterior part . 

 which doe- not descend so low, is separated from t he corpus callosum by a part of t he 

 Subarachnoid space. The base of the fold which slopes downwards and backwards 

 and blends with the upper surface of the tentorium cerebelli. contains the straight 

 sinus running along the line of junction. 



The tentorium cerebelli is a large semilunar fold, concave forwards. It de- 



