606 THE VEINS. 



mater, although these empty themselves into other veins ; in order that wo 

 may be able to consider, in their entirety, all the vessels of the nervous 

 centres which carry dark blood. 



The Sinuses of the Duea Mater in General. — These are vascular 

 spaces comprised in the texture of the external meninge, or situated between 

 that membrane and the bones which form the walls of the cerebro-spinal 

 sheath or even excavated on the inner surface of these bones. These spaces 

 differ more particularly from the veins, by their being generally of a prismatic 

 form, by being continually open, by the absence of valves in their interior, 

 and the presence, in some of them, of lamellas (traheculm), or intersecting 

 iilaments (chordce Willisii) which stud their inner surface, and make them 

 look reticulated. 



Their walls are reduced to an epithelial layer that lies either on the dura 

 mater, or on the osseous tissue. 



It is into these sinuses that the veins of the encephalon and the spinal 

 cord disgorge themselves. 



The Sinuses of the Cranial Dura Mater in Particular. — Four 

 principal will be described : the sinus of the falx cerebri or median sinus, 

 the two cavernous or sphenoidal sinuses, and the group of occipito-atloid 

 sinuses. 



1. Sinus of the Falx Cerebri, oe Median Sinus. — Channeled in the 

 substance of the falx cerebri, and becoming wider as it extends backwards, 

 this sinus commences near the crista galli, and terminates on the internal 

 parietal protuberance by bifurca ting. The two branches resulting from this 

 division form the oris;in of the parieto-temporal confluent, or winepress of 

 SeropMlas (torcular Herophili). 



2. Cavernous ok Supea-sphb n oidal Sinuses. — These are two in number 



a right and a left. They occupy, on the internal face of the sphenoid bone, 

 at each side of the sella turoioa, the so-called cavernous fissures. Bordered 

 outwardly by the superior maxillary nerve, they receive at their anterior ex- 

 tremity the insertion of the alveolar vein. Posteriorly, they join each other, 

 and in doing so form a kind of arch, open in front, around the pituitary 

 gland. Each opens widely at the lacerated foramen, into the subsphenoidal 

 confluent. 



3. Oocipito-atloid Sinuses. —By this name is designated a network of 

 large irregular veins, situated beneath the external face of the dura mater, 

 on the sides of the occipital foramen, and on the entire internal surface 

 of the atloidean ring. Anteriorly, these venous reservoirs communicate, 

 through the condyloid foramen, with the posterior extremity of the sub- 

 sphenoidal confluent. Posteriorly they are continuous with the spinal 

 sinuses, of which we may consider them to be the origin. 



4. Eudimenttart Sinuses of the Cranial Duba Mater,— Independently 

 of the above-described reservoirs, there exist, on the inner wall of the 

 cranium, some rudimentary venous sinuses which should be indicated ; these 

 are : 1, One or two veins lodged in the structure of the tentorium, designated 

 the petrosal or transverse sinuses, communicating, below, with the cavernous 

 sinuses,_and entering, above, into the parieto-temporal confluent ; i 2, Some 

 small, irregular, and reticulated cavities, very variable in their disposition 

 situated beneath the dura mater, on the sides of the cerebellar cavity and 

 which generally empty themselves into the subsphenoidal confluent, by 



> More frequently, perhaps, these veins arise directly from the substance of the brain 

 and do not communicate, below, viith. the cavernous sinuses. 



