THE CEREBRAL GANGLIA. 321 



The cerebral dura mater differs from the spinal in the fact 

 that, its outer surface serving as periosteum, it lacks the layer 

 of loose connective tissue present in the spinal dura mater. 

 Its bulk consists of two layers of dense fibrous tissue running 

 in opposite directions. The inner serous surface is coated with 

 endothelium and lymphatics. The outer or periosteal surface 

 is the most vascular. The cerebral differs from the spinal arach- 

 noid only in being perhaps a little more closely attached to 

 the pia mater. The pia mater of the brain is extremely vascu- 

 lar, and shows more beautifully than the spinal membrane the 

 system of perivascular spaces. 



The cerebral cortex. The cerebral cortex is a thin sheet of 

 gray matter spread on the outer surface of the hemispheres. 

 The outer surface of the hemispheres is grooved by furrows 

 (sulci) less deep in proportion to their size, and less regular 

 than those of the cerebellum. The convolutions produced by 

 these sulci, although seemingly very irregular, still have a cer- 

 tain symmetry in different brains by which they can be classi- 

 fied and named. A definite knowledge of these facts is neces- 

 sary for an understanding of the current literature on the 

 subject and of properly recording cases. 



The fetal hemisphere at an early date is smooth. Furrows 

 soon begin to appear, the first and most important of which is 

 the fissure of Sylvius, extending upward and backward, from 

 about the anterior third of the base of the brain, and the fis- 

 sure of Rolando, running from near the posterior extremity of 

 the fissure of Sylvius upward to the superior longitudinal fis- 

 sure. One after another the other fissures appear, till in the 

 adult brain they seem innumerable. Even here, however, there 

 is a certain constant arrangement of fissures and convolutions 

 on which a nomenclature may be based. 



The original fissures of Sylvius and Rolan do remain. From 

 the anterior inferior part of the frontal lobe three furrows run 

 obliquely upward and backward toward the two fissures just 

 named, dividing the frontal region into the three frontal con- 

 volutions, while a convolution in front of the fissure of Rolando 

 receives the name of the ascending frontal or anterior central 

 convolution. A similar convolution behind the fissure is called 

 the ascending parietal or posterior central convolution. The 

 parietal region is irregularly divided from above downward, 

 as is also the temporo-sphenoidal and occipital region. The 



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