EXTRACT XLIX. B. 



ON THE MENINGEAL COVERINGS OF THE BRAIN 

 AND SPINAL CORD. 



THE meninges of the brain and spinal cord, with the 

 neurilemmar coverings of the nerves, being so intimately 

 connected with the nerve structures proper, and with the 

 economy of their lymph circulation, call for a word of 

 description, in order to provide for a more complete 

 continuity of view of the broken subjects, although, we 

 hope, somewhat connected narrative of our studies. The 

 most external of these meningeal coverings, the dura 

 mater i so named from its dense and unyielding texture, 

 lines the cranial cavity, to the bones of which it is most 

 intimately united by a thick-set series of fibrous projections, 

 and constitutes the internal periosteum of the skull ; at 

 different points of the ridges and surfaces, of which it 

 splits up to form the venous channels or sinuses, and 

 projects itself under and between the various divisions 

 and hemispheres of the cerebrum and cerebellum, the 

 proper anatomical position and relationships of which it 

 largely assists in maintaining after which it leaves the 

 cranial cavity by way of the foramen magnum^ where its 

 external layer becomes continuous with the pericranium, 

 while its internal layers are continued along the spinal 

 canal to its extremity, whence it is emitted as the sub- 

 stance and enclosing layer of the structure known as the 

 filum terminale, until, as we think, its junction with the 

 glandular body denominated coccygeal. Throughout all 

 this extent its texture is histologically continuous, being 

 one and indivisible, save for the numerous openings, or 



