DUEA MATER. 571 



is received into the longitudinal fissure between the two hemispheres of 

 the cerebrum. This is the falx cerelri. The second is an arched or 

 vaulted partition, stretched across the baclv part of the skull, between 

 the cerebrum and the cerebellum ; it is named the tentorium corehelK. 

 Below this, another vertical partition, named falx cnelelti, of small 

 extent, passes down between the hemispheres of the cerebelhim. 



The fatx. cerelni is narrow in front, where it is fixed to the crista 

 galli, and broader behind, where it is attached to the middle of the 

 upper surface of the tentorium, along which line of attachment the 

 straight sinus is situated. Along its upper convex border, which is 

 attached above to the middle line of the inner surface of the cranium, 

 runs the superior longitudinal sinus. Its under edge is free, and reaches 

 to within a short distance of the corpus callosum, approaching nearer 

 to it behind. This border contains the inferior longitudinal sinus. 



The tentorium, or tent, is elevated in the middle, and declines down- 

 wards in all directions towards its circumference, thus corresponding in 

 form with the upper surface of the cerebellum. Its inner border is 

 free and concave, and leaves in front of it an oval opening, through 

 which the isthmus encephali descends. It is attached behind and at 

 the sides by its convex border to the horizontal part of the crucial 

 ridges of the occipital bone, and there encloses the lateral sinuses. 

 Farther forward it is connected v.'ith the upper edge of the petrous 

 portion of the temporal bone — the superior petrosal sinus running 

 along this line of attachment. At the point of the pars petrosa, the 

 external and internal borders meet, and may be said to intersect each 

 other — the former being then continued inwards to the posterior, and 

 the latter forwards to the anterior clinoid process. 



The falx cexeltelli (falx minor) descends from the middle of the 

 posterior border of the tentorium, with which it is connected, along 

 the vertical ridge named the internal occipital crest, towards the fora- 

 men magnum, bifurcating there into two smaller folds. Its attach- 

 ment to the bony ridge marks the course of the posterior occipital sinus, 

 or sinuses. 



Structure. — The dura mater consists of white fibrous and elastic 

 tissue, arranged in bands and laminre, crossing each other. In the 

 spinal dura mater the bundles have a more nearly parallel arrangement. 

 A layer of pavement epithelium exists upon its inner surface, which 

 was formerly regarded as belonging to the serous membrane lining it. 

 A similar layer of epithelium also covers ])oth sides of the spinal dura 

 mater. The cranial membrane is traversed by numerous blood-vessels 

 which are chiefly destined for the bones. An extensive system of lymph 

 canals has been described, formed cliiefly by the spaces between the 

 fibrous trabeculaj, and bounded by cellular membranes. Minute nervous 

 filaments, derived fi-om the fourth, fifth, and eighth cranial nerves, and 

 from the sympathetic, are described, as entering the dura mater of the 

 brain. Nervous filaments have likewise been traced in the dura mater 

 of the spinal column. (Luschka and Rildinger, quoted by Hyrtl.) 



THE PIA MATER. 



The -fia mater is a delicate, fibrous, and highly vascular membrane, 

 which immediately invests the brain and spinal cord. 



Upon the hemispheres of the brain it is applied to the entire cortical 

 surface of the convolutions, and dips into all the sulci, which thus 



