SYSTEMATIC SYNTHESIS OF TISSUES INTO ORGANS. 273 



655. Upon the subarachnoi- Fia 189> 

 dean tissue, as upon a hydrosta- 

 tic bed, THE BRAIN is PROTECTED 



from the least effect of the jars 

 sent up through the body. In 

 old age, in the thickest part, 

 this has become an inch thick. 

 (See a, adjoining Fig.) 



656. THE BRAIN is FULLY 

 PROTECTED by the curved, arch- 

 ed, and irregular form of the 



skeleton, and by the flexures of the joints by which jars 

 are dispersed ; by the cartilages of the joints ; by the 

 spongiform structure of the bones and the marrow they 

 contain ; by the subarachnoidean cushion ; by the arched 



FIG. 190. 



Fig. 190 represents the 

 cerebri sliced down to the 

 upper surface of 4, the 

 bridge (corpus callosum) 

 of fibres that extends across 

 from one to the other. 5, 

 5, are the deep fissures be- 

 hind and before, that ex- 

 tend up between the 

 parts removed ; the bottom 

 of the middle part of the fis- 

 sure is represented length- 

 wise the centre of 4. This 

 fissure is occupied by the 

 falx, the lower edge of the 

 central part of which 

 touches 4, the ends sink- 

 ing down at 5, 5. 1 is the 

 white tissue, its fibres be- 

 ing interlaced by fine sin- 

 ewy fibres ; the dots show 

 sections of a few capillaries 

 extending among them ; 2, 

 the gray tissue, the dark line indicating the anfractuosity or the division 

 of capillaries between touching portions of the surface of the gray Tissue. 



Describe Fig. 189. 655. From what ? 656. Enumerate the means by which 

 Describe Fig. 190. 



12* 



