112 



PHYSIOLOGY. 



volutions, and also forms a sheath for all nerves or blood- 

 vessels that pass out of, or into the brain. 1 



a. The scalp, turned down. 



b. The cut edge of the bones of the skull. 



e. The external strong membrane of the brain, (dura mater) ui 

 pended by a hook. 



d. The left hemisphere of the brain, showing its convolutions. 



e. The superior edge of the right hemisphere. 

 /. The fissure between the two hemispheres. 



7., The pia mater is a loose cellular membrane, composed 

 chiefly of blood vessels, which dips into all the fissures, and 

 wraps round all the convolutions of the brain. The chief 

 use of these membranes seems to be to support the different 

 parts of the brain in their respective places, so that they may 

 not be injured by sudden shocks and jars, or by compression ; 



