DURA MATER OP THE BRAIN. 393 



These several divisions are all covered by membranes 

 which are common to the whole, and are the same as those 

 of the spinal marrow, the dura mater, the tunica aracli- 

 noidea, and the pia mater. It is only necessary for us 

 to point out the peculiarities of these membranes as per- 

 taining to the brain. 



Dissection. Make an incision through the scalp, from 

 the ear upon the one side, across the vertex to the opposite 

 ear ; turn the skin over the face in front, and upon the 

 neck behind ; now with the saw carry a circular incision 

 through the first table of bone, commencing about an inch 

 above the superciliary arches, and terminating a little be- 

 low the external occipital protuberance. A few blows with 

 mallet and chisel will separate the internal table, and the 

 calvarium can be readily removed. The brain should now 

 be removed from the cavity of the cranium, which can be 

 done by commencing at the anterior part, and gently rais- 

 ing it from the base of the skull, dividing from before, 

 backward, each nerve and vessel in succession,, close to the 

 bone ; divide the tentoriurn, and cut the spinal marrow as 

 low in the neck as can be reached, when the brain can be 

 removed. 



Dura Mater. The dura mater of the brain is continuous 

 with that of the spinal marrow, is of great strength, and 

 performs no less than five different offices : first, it acts as 

 a periosteum to the inner surface of the cranium ; second, 

 it gives a secure covering to the brain, especially needed 

 in early life when the bones are separated ; third, it sends 

 in processes which divide and support the different parts 

 of the brain ; fourth, it forms the different sinuses ; and 

 fifth, it gives sheaths to the several nerves as they leave 

 the cranium. Its external surface has a strong adhesion to 

 the internal surface of the cranium, so that it presents a 

 rough appearance from the rupture of vessels and fibres 

 connecting the two. The adhesion is strongest at the base, 

 and along the course of the sutures. It adheres to the 

 lesser wings of Ingrassias, the petrous edge of the temporal 

 bone, sends processes through the several foramina of the 



