THK DURA OF THE BRAIN 



969 



Along the middle line of its upper surface the posterior border of the falx is attached, 

 the tentorial or straight sinus being placed at their point of junction. Its frontal 

 border is free and concave, and with the dorsum sellae forms a large oval opening. 

 This opening is called the incisura tentorii and transmits the mesencephalon. 



The falx cerebelli (falculq) (Fig. 718) is a small triangular process of dura 

 received into the indentation between the two lateral lobes of the cerebellum 

 behind. Its base is attached, above, to the under and back part of the tentorium 

 cerebelli; its posterior margin, to the lower division of the vertical crest on the 

 inner surface of the occipital bone. As it descends it sometimes divides into two 

 smaller folds, which are lost on the sides of the foramen magnum. 



The diaphragma sellae (Fig. 718) is a small, circular, horizontal fold, which 

 constitutes a roof . for the sella turcica. This almost completely covers the 

 hypophysis, presenting merely a small central opening (foramen diaphragmatis 

 sellae) for the passage of the infundibulum. 



Structure (Fig, 717). The dura consists of white fibrous tissue with connective-tissue 

 cells and elastic fibres arranged in flattened laminae, which are imperfectly separated by lacunar 

 spaces and bloodvessels into two layers, endosteal and meningeal. The endosteal layer is 

 the internal periosteum for the cranial bones and contains the bloodvessels for their supply 



SUPERIOR LONGI- 

 TUDINAL SINUS 



FALX CEREBR. 



TENTORIUM 

 CEREBELLI 



FALX CEREBELLI 



FlG 720.- 



-Crucial prolongation of the dura. Frontal section passing through the tentorium cerebelli. 

 torcular herophili is seen in the centre. (Poirier and Charpy.) 



The 



At the margin of the foramen magnum it becomes continuous with the periosteum lining the 

 vertebral canal. The meningeal or supporting layer is lined on its inner surface by a layer of 

 nucleated endothelium, similar to that found on serous membranes. By its reduplication the 

 meningeal layer forms the falx cerebri, the tentorium cerebelli and falx cerebelli, and the 

 diaphragma sellae. The two layers are connected by fibres which intersect each other obliquely. 



The arteries of the dura (see section on Arteries) are very numerous, but are chiefly distributed 

 to the bones. Those found in the anterior fossa are the anterior meningeal branches of the 

 anterior and posterior ethmoidal and internal carotid, and a branch from the middle meningeal. 

 Those in the middle fossa are the middle and small meningeal branches of the internal maxil- 

 lary; a branch from the ascending pharyngeal, which enters the skull through the foramen 

 lacerum medium; branches from the internal carotid, and a recurrent branch from the lac- 

 rimal. Those in the posterior fossa are meningeal branches from the occipital, one of which 

 enters the skull through the jugular foramen, and the other through the mastoid foramen; the 

 posterior meningeal from the vertebral; occasional meningeal branches from the ascending 

 pharyngeal, which enter the skull through the jugular and anterior condylar foramina; and a 

 branch from the middle meningeal. 



The veins which return the blood from the dura (see p. 719), and partly from the bones, 

 anastomose with the diploic veins (see p. 730). They terminate in the various sinuses, with the 

 exception of two which accompany the middle meningeal artery, and pass out of the skull at the 

 foramen spinosum to join the internal maxillary vein; above, the meningeal veins communicate 

 with the superior longitudinal sinus. The sinuses are considered on pages 723 to 730 inclusive. 



