STRUCTURE Or THE BRAIN. 207 



any other organ. It would therefore be entirely 

 out of place to attempt to describe it here, further 

 than by stating generally its principal divisions. 

 On sawing off the top of the scull, and removing the 

 firm tough membrane called dura mater (hard mo- 

 ther), which adheres closely to its concave surface, 

 the cerebrum, or brain proper, presents itself, marked 

 on the surface with a great variety of undulating 

 windings or convolutions, and extending from the 

 fore to the back part of the head, somewhat in the 

 form of an ellipse. In the middle line, a deep fissure 

 is perceived, into which dips a fold of the dura 

 mater, named the falx, separating the brain, in its 

 whole length, into two halves, or hemispheres, as 

 they are called. Each hemisphere is, in its turn, 

 divided, but in a less marked way, as the divisions 

 are observable only on its inferior surface, into 

 three portions, called, from their situations, the an- 

 terior, middle, and posterior lobes, each occupying 

 nearly a third of the whole length of the brain. 

 The anterior lobe occupies the forehead ; the Twiddle 

 is all the portion of brain lying above and a Sittle in 

 front of the ears ; and the posterior fills the back 

 part of the head. 



Beneath the posterior lobe, a strong fold of the 

 dura mater, called the tentorium, is extended hori- 

 zontally to support and separate it from the cerebel- 

 lum, or little brain lying below it. The cerebellum 

 forms the last great division of the contents of the 

 scull. Its surface is marked by convolutions, diifer- 

 ng, however, in size and appearance from those ob- 

 served in the brain. 



Adhering to the surface of the convolutions, and 

 consequently dipping down into and lining the sulei 

 or furrows between them, another membrane, of a 

 finer texture, and great vascularity, called the pia 

 mater, is found. The blood-vessels going to the brain 

 branch out so extensively on the pia mater, that, 

 *-hen a little inflamed, it seems to constitute a pei . 



