OF EVOLUTION. 75 



we are brought to an astonishing result when 

 a study is made of the brains of the earlier 

 animals, the outlines of many of which have been 

 as perfectly preserved as the casts of the interiors 

 of shells. From this study it appears that all 

 the Tertiary mammals had comparatively small 

 brains, and that there has been a gradual increase 

 in the size of the brain mass from the earlier to the 

 later parts of this period, the increase being almost 

 wholly confined to the cerebral hemispheres. In 

 the earlier forms indeed, until late in the Terti- 

 ary the hemispheres left the cerebellum entirely 

 uncovered, and the olfactory lobes were corre- 

 spondingly largely developed. The brain was, in 

 fact, more nearly reptilian in character than mam- 

 malian. The series of diagrams before you illus- 

 trate the development of the brain in certain 

 mammals of the Tertiary period more or less 

 closely connected in their ordinal relations. 



It wifl be seen from these figures that the 

 relative size of the brain in the older mam- 

 malian types was small when compared with 



