ii THE POSTERIOR LOBES. 135 



completely fills the cranial cavity, it is obvious 

 that a cast of the interior of the skull will repro- 

 duce the general form of the brain, at any rate 

 with such minute and, for the present purpose, 

 utterly unimportant differences as may result from 

 the absence of the enveloping membranes of the 

 brain in the dry skull. But if such a cast be made 

 in plaster, and compared with a similar cast of the 

 interior of a human skull, it will be obvious that 

 the cast of the cerebral chamber, representing the 

 cerebrum of the ape, as completely covers over and 

 overlaps the cast of the cerebellar chamber, repre- 

 senting the cerebellum, as it does in the man (Fig. 

 21). A careless observer, forgetting that a soft 

 structure like the brain loses its proper shape the 

 moment it is taken out of the skull, may indeed 

 mistake the uncovered condition of the cerebel- 

 lum of an extracted and distorted brain for the 

 natural relations of the parts; but his error must 

 become patent even to himself if he try to replace 

 the brain within the cranial chamber. To suppose 

 that the cerebellum of an ape is naturally uncov- 

 ered behind is a miscomprehension comparable 

 only to that of one who should imagine that a 

 man's lungs always occupy but a small portion of 

 the thoracic cavity, because they do so when the 

 chest is opened, and their elasticity is no longer 

 neutralized by the pressure of the air. 



And the error is the less excusable, as it must 

 become apparent to every one who examines a sec- 



