TO THE LOWER ANIMALS 281 



the skull, may indeed mistake the uncovered condition of 

 the cerebellum 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 uncovered 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 section of the skull 

 of any ape above a Lemur, without taking the trouble to 

 make a cast of it. For there is a very marked groove in 

 every such skull, as in the human skull which indicates 

 the line of attachment of what is termed the tentorium 

 a sort of parchment-like shelf, or partition, which, in the 

 recent state, is interposed between the cerebrum and 

 cerebellum, and prevents the former from pressing upon 

 the latter (see Fig. 16). 



This groove, therefore, indicates the line of separation 

 between that part of the cranial cavity which contains the 

 cerebrum, and that which contains the cerebellum ; and 

 as the brain exactly fills the cavity of the skull, it is obvious 

 that the relations of these two parts of the cranial cavity 

 at once informs us of the relations of their contents. Now 

 in man, in all the old-world, and in all the new- world Simise, 

 with one exception, when the face is directed forwards, this 

 line of attachment of the tentorium, or impression for the 

 lateral sinus, as it is technically called, is nearly horizontal, 

 and the cerebral chamber invariably overlaps or. projects 

 behind the cerebellar chamber. In the Howler Monkey or 

 Mycetes (see Fig. 16), the line passes obliquely upwards 

 and backwards, and the cerebral overlap is almost nil ; 

 while in the Lemurs, as in the lower mammals, the line is 

 much more inclined in the same direction, and the cere- 

 bellar chamber projects considerably beyond the cerebral. 



When the gravest errors respecting points so easily 

 settled as this question respecting the posterior lobes can 

 be authoritatively propounded, it is no wonder that matters 

 of observation, of no very complex character, but still 

 requiring a certain amount of care, should have fared 

 worse. Any one who cannot see the posterior lobe in an 



