916 



THE NERVOUS SYSTEM 



noid, and its medial border forms the boundary of the foramen of the diaphragma 

 sellce and surrounds the infundibulum. Its superior surface is in relation with the 

 base of the brain, and its inferior surface is in relation with the hypophysis, which 

 it binds down in the hypophyseal fossa. 



The spaces which lie between the layers of the cranial dura mater are Meckel's 

 caves, the spaces which lodge the endolymphatic sacs, and the blood sinuses and 

 lacunae. 



Meckel's caves are two cleft-like spaces or niches which lie, one on each side, 

 in the trigeminal impression on the apex of the petrous portion of the temporal 

 bone. Each space lodges the semilunar (Gasserian) ganglion and the trigeminus 

 and masticator nerves of the corresponding side, and it communicates with the 

 subdural space in the posterior fossa of the cranium by an oval opening, which lies 

 above the superior border of the petrous portion of the temporal bone and inferior 

 to the superior petrosal sinus. 



Fig. 722. — Showing Blood-vessels of Cranial Dura Mater and Cranial Nerves in the 



Base of the Skull. 

 (On the left side the dura mater has been removed from the middle fossa.) 



Meningeal branch of an- 

 terior ethmoidal artery 



Meningeal branch of pos" 

 terior ethmoidal artery 



Middle meningeal 

 artery 

 Ophthalmic division of 

 trigeminus 



Oculomotor nerve 



Cavernous sinus 



Trochlear nerve 



Auditory and facial 



nerves 



Superior petrosal sinus 



Inferior petrosal sinus 



Petro -squamous sinus 



Spinal accessory nerve 



Sigmoid sinus 



Posterior meningeal 

 branch of vertebral 

 artery 



Left marginal sinus 



Left transverse sinus 



Superior sagittal sinus 



Circular sinus 

 Carotid artery 

 Abducens 

 Basilar artery 

 Basilar plexus of 



veins 



Auditory artery 



Vertebral artery 



f-Glosso - pharyngeal 



and vagus nerves 



Anterior spinal 



artery 

 Hypoglossal nerve 

 Spinal accessory 

 nerve 



Right marginal sinus 



Occipital sinus 

 — Right transverse sinus 



The space which contains the endolymphatic sac on each side lies behind the 

 petrous portion of the temporal bone and communicates with the aquaeductus 

 vestibuli. 



The venous sinuses and lacunae. — The cranial blood sinuses have already been fully 

 described in the account of the vascular system, and it is sutHcient to note here that they are 

 <;ontinuous, on the one hand, with the meiiinjjieal veins, and, on the other, with the veins outside 

 the cranial walls. The vessels which establish communication between the blood sinuses and 

 the extracranial veins are referred to collectively as emissary veins. They possibly help to 

 maintain the regularity of the cranial circulation, and they have therefore a certain amount of 

 practical importance. 



The sinuses which are connected with the extracranial veins by emissary veins are the 

 superior sagittal, the transverse (lateral), and the cavernous. Three or four emissary veins 

 pass from the superior sagittal sinus: — one passes through the foramen caecum and communicates 

 with the veins of the roof of the nose, or, through the nasal bones, with the angular veins. 

 Two pa.ss through the parietal foramina and establish communications with the occipital 

 veins, and a fourth, which is very inconstant, pierces the occipital protuberance and joins the 

 tributaries of the occipital veins. Connecting each lateral sinus with the extracranial veins 



