PREFACE. XV11 



The third leading modification of the mammalian cerebrum is 

 such an increase in its relative size that it extends over more or 

 less of the cerebellum, and generally over more or less of the 

 olfactory lobes. Except in a few inferior forms of the Quadrumana 

 the superficies is folded into convolutions, whence this third sub- 

 class is named Gyrencephala. As a general rule there is a scro- 

 tum; the vulva is externally distinct from the anus. With the 

 exception of the elephants, there is a single anterior cava. 



In man the hemispheres overlap the olfactory lobes and the 

 cerebellum; their posterior large development includes the posterior 

 horn of the lateral ventricle and the hippocampus minor. Man forms 

 a distinct sub-class, Archencephala. 



For the definitions of the secondary groups of these four pri- 

 mary diseases the memoir itself is referred to. 



Prof. OWEN'S Table of the Subclasses and Orders (reversed to 

 facilitate comparison with the arrangement of the present work) is 

 annexed. 



w.c. 



CAMBRIDGE, 



Feb. 10, 1858. 



