674 



THE XER VOL'S SYSTEM 



which usually jtiorce the great wing of the sphenoid near the outer angle of the sphenoidal fis- 

 sure, lu the middle craiiial fossa tlie following arteries are uiet with: a branch of the ascending 

 pharyngeal which i)erforates the cartilage which occupies the foramen laccruni medium ; the 

 meningea parva which enters the cranium through the foramen ovale ; the meningeal branch of 

 the iiitcriiul carutiil. and twigs from the middle meningeal. In the po.-terior cranial fossa, two 

 meningeal branches, derived i'rom the occii)ital and ascending pharyngeal, enter through the 

 posterior compartment of the jugular foramen, another twig from the oiripital pas.ses through 

 the mastoid foramen, and a twig from the ascending i)haryngeal makes its way through the ante- 

 rior condyloid foramen. A meningeal branch of the vertebral is given off from that artery, in 

 the interval between the occipital bone and the posterior arch of the atlas, and enters the skull 

 through the foramen magnum. 



A branch of the occipital artery (ramus parietalis, Cruveilhier) occasionally passes through 

 the parietal foramen to the dura mater lining the calvaria. 



The following are the infoklings formed l;)y the inner or siti)])orting layer of the 

 dura mater, taken in their order of magnitude: the falx cerebri, the tentorium 



Fig. 404. 



-CoROXAL Section of the Head passing through the Posterior Horns of 

 THE Lateral Ventricles. 



(From a mounted specimen in the Anatomical Department of Triuit}- College, Dublin.) 



Dura mater 



BULB OF 



POSTERIOR 



CORXU 



HIPPOCAM- 

 PUS MINOR 



FASCICULI'S 

 LONGITUDI- 

 NALIS IN- 

 FERIOR 



Superior 

 longitmiinal 

 sinus 



Falx cerebri 



Straight sinus 



POSTERIOR 

 CORNU OF 

 LA TERA L 

 lENTRICLE 



CALCARINE 

 FISSURE 



Lateral sinus CORPUS DENTA TUM Tentorium cerebelli 



cerebelli, the falx cerebelli, and the diaphragma sellae. There are also two 

 smaller ])aired fokls; viz. the folds which project from the lesser wings of the 

 s})henoid l)one into the Sylvian fissures of the brain, and the crescentic folds which 

 are ])laced over the optic nerves at the upper margin of the optic foramina. 



The Falx Cerebri is a large sickle-sha})ed process, deeper liehind than in front, 

 which is placed in the great longitudinal iissure of the brain. It is attached by its 

 base to the tentorium cerebelli, in the middle line, and maintains l)y its tension the 

 vaulted character of the latter. The straight sinus follows this line of attachment. 

 Its apex is firndy fixed to the crista galli of the ethmoid, and has also an attach- 

 ment to the ethmoidal spine of the sphenoid bone. Its convex or upper margin 

 corres})onds to the superior longitudinal sinus, and is attached to the periosteal 

 layer opposite to the edges of the groove for that sinus in the frontal, the two 

 parietal, and the occipital bones. The inferior longitudinal sinus courses along 

 its concave or free margin. This margin closely a])iu-oaches the corjius callosiun 

 Itchind, but is separated from it by a considerable interval in front. 



