STRUCTURE OF THE DURA MATER. 



183 



of the temporal bone the superior petrosal sinus running along this line of attach- 

 ment. 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 cerebelli (falx minor, fig. 12!), 13) descends from the middle of the 

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



7- 



Fig. 129. THE CRANIUM OPENED TO SHOW THE FALX OF THE CEREBRUM AND TENTORIUM OP THE 



CEREBELLUM, AND THE PLACES OF EXIT OF THE CRANIAL NERVES. (Sappey. ) \ 



1, falx ; 2, superior longitudinal sinus ; 3, concave border of the falx ; 4, inferior longitudinal 

 sinus ; 5, base of the falx ; 6, straight sinus ; 7, anterior part of the falx ; 8, right side of the ten- 

 torium cerebelli, seen from below ; 9, lateral sinus ; 10, superior petrosal sinus ; 11, inferior petrosal 

 sinus ; 12, posterior occipital sinus ; 13, falx cerebelli ; 14, 15, 16, 17, 18, second, third, fourth, 

 fifth, and sixth cranial nerves ; 19, seventh and eighth nerves ; 20, ninth, tenth, and eleventh 

 nerves ; 21, twelfth nerve ; 22, 23, first and second cervical nerves ; 24, upper end of the ligamentum 

 denticulatum. 



ridge named the internal occipital crest towards the foramen magnum, bifurcating 

 there into two smaller folds. Its attachment to the bony ridge marks the course of 

 the occipital sinus or sinuses. 



Structure. The dura mater consists of white fibrous and elastic tissue, arranged 

 in bands and laminae, those of the two layers crossing each other obliquely for the 

 most part in the cranial dura mater. In the falx and tentorium the bundles 

 are arranged radially. It is not uncommon to find the cranial dura mater 

 ossified in parts : most commonly in the falx cerebri. In the spinal dura mater the 

 bundles have a nearly longitudinal arrangement. A layer of flattened endothelial 

 cells covers its inner surface, and also its outer surface between the places of 

 adherence to the bones and sutures. A similar layer of cells also covers both sides 

 of the spinal dura mater. The cranial membrane is traversed by numerous blood- 

 vessels which are chiefly destined for the bones, but there is a wide-meshed capillary 

 network with peculiar ampullary enlargements, distributed near the inner surface of 

 the cranial dura mater, and another network near the outer surface. The spaces 

 between the fibrous trabeculse contain flattened connective tissue corpuscles which 



