34 



PHYSIOLOGY AND MORPHOLOGY OF ANIMALS. 



and runs along its base, forming successive swellings 

 and outgrowths in its course forward. First the me- 

 dulla with its outgrowth, the cerebellum, then the optic 



lobes with their four swell- 

 ings atop, then the thala- 

 mus with its four swellings, 

 and lastly the cerebrum; 

 but this last has grown 

 backward and covered all 

 the other parts and thus 

 obscured the real structure 

 of the brain. This will come 

 out more clearly presently. 

 Convolutions of the 

 Brain. — The surface of the 

 cerebrum is diversified with 

 irregular folds (convolu- 

 tions) with deep trenches 

 between. Into the trenches 

 enter the pia mater, but not 



Fig. 18— A cross-section of the lifted the dura mater Thprp an» 

 cerebrum: Longitudinal section e UUrd mater - 1 nere are 



of the cerebellum, showing optic a few larger trenches called 



lobes, ol \ thalamus and corpora r 



striata, th. After Daiton. ' fissures dividing the cere- 



bral hemispheres into lobes. 

 The most conspicuous of these is the fissure of Sylvius 

 (Fig. 16, s). It commences well forward, runs backward 

 and upward, separating the posterior lobe from the rest 

 of the cerebrum. Another is the fissure of Rolando (Fig. 

 16, ;-), which separates the rest of the cerebrum into two 

 parts. By these two fissures the cerebrum is divided 

 into three lobes — anterior, middle, and posterior, or 

 frontal, parietal, and occipital. 



The cerebellum is convoluted also, but in a more 

 regular way, being deeply separated into parallel lami- 

 nae or leaves. All the other parts are smooth. 



