270 DETAILED SYNTHESIS. 



FRACTUOSITIES is a network of minute capillaries sup- 

 ported by a small number of delicate sinewy fibres called 

 the pia mater. 



640. FROM THE pia mater STILL SMALLER CAPILLARIES 



EXTEND INTO THE STRUCTURE BELOW, Supplying it Still 



more intimately and abundantly with nutritious blood. 

 On the other hand, veins lead from the pia mater direct- 

 ly into the sinuses or large veins of the lining of the 

 skull, in order that the Blood may flow rapidly away, 

 and do not follow back a more tortuous path along- 

 side the arteries, as is the case elsewhere ; this shows 

 the importance of a free passage from the brain of its 

 waste material. 



641. A VIEW OP THE BRAIN FROM ABOVE SHOWS it 

 divided on the central line by a deep fissure, in which is 

 the membrane called the falx (36, Fig. 160), into what 

 are called the right and left hemispheres, or right and 

 left Brains. 



642. AN EXAMINATION OF THE SIDES OF THE FISSURE 



lying against the falx, DETERMINES that the convolutions 

 and anfractuosities exist there as well as externally. 



643. THE CONVOLUTIONS ARE NOT EXACTLY ALIKE in 

 the two sides, much less in two persons ; and thus is sus- 

 tained what was said, that form, etc., are not essentials. 



644. By removing the side of the skull, and VIEW- 

 ING THE BRAIN AT THE SIDE, IT WILL APPEAR to be con- 

 structed of two parts, one, about one eighth the size of 

 the whole, being situated under the back part of the 

 other, and separated from it by a partition or shelf. The 

 larger is called the cerebrum, and the smaller the cere- 

 bellum. 



645. THE CEREBELLUM has a more even external 

 surface than the cerebrum, and a shallow groove at its 

 back part, on the middle line, occupied by a membrane 

 corresponding to the falx. 



640. Why do - ? 641. What does ? Describe falx, Fisr. 160. 642. What does 

 ? 648. Where are ? 644. What ? 645. What said of ? 



