PLATE XLIX. NATURAL SIZK. 



INTERIOR OF SKULL WITH TENTORIUM REMOVED AND 

 DEEP VIEW OF ORBITS, GASSERIAN GANGLION, AND 

 PTERYGOID REGION FROM ABOVE. 



This dissection is a deeper one on the same body as the preceding, only the tentorium 

 has been completely removed and the lateral sinus opened up in the whole of its course. 

 The dura mater of the middle fossa forming the roof of Meckel's space has been turned 

 back to expose the Gasserian ganglion. On the right side the floor and side of the 

 middle fossa has been cut away to expose the external pterygoid muscle from above with 

 the course of the masseteric and deep temporal nerves. 



The lati>nil sinuses, if examined, will be found to be unequal in size, the right being 

 usually the larger ; it generally receives the blood from the superior longitudinal sinus, 

 i.e. the chief part of the blood from the surface of the brain, while the left and smaller 

 usually ri-ci'ivi'S the straight sinus, which again takes the blood from the central ganglia. 

 Jn the early foetal condition the lateral sinuses empty chiefly into the external jugular 

 through the mastoid foramen, but as development proceeds this gradually lessens, the 

 internal jugular becoming developed as the chief means of exit. 



The Emissary veins are those which communicate through apertures in the skull 

 both with the veins within and those without. The chief are : 



1. Through the foramen caecum between the superior longitudinal sinus and veins 

 of the nose ; this is often obliterated in adults. 



2. Through the parietal foramen between the superior longitudinal sinus and veins 

 of the scalp. 



8. Through the occipital protuberance between the Torcular Herophili and the 

 occipital vein. 



4. Through the mastoid foramen between the lateral sinus and posterior external 

 jngnlar. 



5. Through the posterior condyloid between the lateral sinus and posterior vertebral 

 vein. 



6. Through the anterior condyloid between the occipital sinus and the deep veins 

 of the neck. 



7. Through foramen Vesalii or foramen ovale, between the cavernous sinus and 

 the veins of the pterygoid plexus. 



8. Through small veins around the carotid artery the cavernous plexus communi- 

 - with the internal jugular. 



9. Although hardly an emissary vein, a communication exists between the 

 ophthalmia vein and the angular, thus connecting the cavernous sinus with the facial 

 vein. 



10. A communication exists between the occipital sinus and the posterior spinal 

 veins ; this again is barely an emissary vein in the correct sense of the term. 



11. A communication exists between the cavernous sinus and the veins outside the 

 base of the skull through the foramen lacerum medium. 



12. A pair of veins usually pass through the foramen spinosum to communicate 

 between the meningeal veins and the veins of the exterior. 



18. There is sometimes a vein passing through the foramen rotundum. 



