MEXrXOES 673 



continuous with tlic dura niatcr of the spinal cord. Tlic periosteal layer clothes 

 the bone and is thickened into a ligamentous band, the occipito-cervical or cervico- 

 basilar ligament (page 188), Avhich passes through the foramen magnum to join the 

 posteiior connnon ligament of the vertebne and to gain attachment to the l>o(.ly of the 

 axis. Thus a connection is established between the dura mater and the jieriosteum 

 of the vertebra\ At the l)ack and sides of the foramen magnum the dura mater 

 does not split into periosteal and supporting layers until it reaches the margin of 

 that opening, where its layers divaricate, the one to become continuous with the 

 external periosteum of the skull, the other to be continued into the spinal dura 

 mater. In the middle fossa of the skull there is a separation of the periosteal and 

 supi)orting layers to form the cavernous sinus; on the inner side of this the sup- 

 ])orting layer is moulded round the pituitary body and then folds on itself to form 

 the diaphragma sellae which roofs in the pituitary fossa. External to the 

 cavernous sinus the two layers remain separate for some distance, forming a space 

 (Meckel's space), which encloses the Gasserian ganglion. The outer surface of 



Fig. 403. — Coronal Section of the Head passing thkough the Mastoid Process. 

 (From a mounted specimen in tbe Anatomical Department of Trinity College, Dublin.) 



•Superior longi- 

 tudinal sinus 



Falx cerebri 



CORPUS 

 f'ALLOHVM 



Choroid plexus 

 i'eins o/ Galen 



Tentorium 

 eerebelli 



Lateral .sinus 



f OR PIS 

 DENTA TIM 



CA IDA TE 

 M'CLEIS 



LATERAL 

 VEyfRICLE 



Superior petrosal 



sinus 

 MASTOID ANTRUM 



Lateral sinus 



MASTOID PROCESS 



the dura mater is covered with a number of arteries, which ramify between it and 

 the inner table of the skull. These vessels break up into small twigs which 

 penetrate the bone. The term meningeal, a])i»lied to the arteries in question, is 

 somewhat misleading, inasmuch as they do not sujijily any of the meninges, except 

 the dura mater, being chiefly destined for the nutrition of the cranial bones. These 

 small vessels, together with a number of fibrous retinacula, are torn across when 

 the dura mater is forcibly detached from the bone, and give rise to the rough 

 appearance which is presented by its outer surface. An examination under water 

 will, however, reveal smooth s])ots interspersed among the bundles of ruptured 

 vessels; these are subperiosteal lymph-spaces. 



