62 DINOCEUATA. 



The small size of the brain in early Tertiary niannnals will be 

 indicated by an examination of the Dhiocerata skulls, with the brain in 

 position, shown in figures 57 and 68, page 54. This is further shown by 

 figure QQ, page 63, which represents the skull and brain of Coryphodon, 

 the largest mammal in tlie lower Eocene, from beds of earlier age than 

 those containing the Dinocerafa, as shown in the section, figure 2, page 7. 



The size of the brain in the middle Eocene genera PaJceosijops, 

 Lijmnohyus, (_'<jJoiioceras, and Hyrachyus are shown in figures C8 to 71, 

 pages 63 and 64. Aiiu/nodoii from the upper Eocene is represented in 

 figure 72, page 64. 



The larger brain of the Miocene mammals is indicated by the figure 

 64, page 61, i-epresenting the skull of Brotitofheriioii, which is found at the 

 base of the Miocene, as shown in figure 2, page 7. JElotherium from the 

 same horizon is represented in figure 75. The skull of Eporeodon, with its 

 brain in jiosition, figure 73, page 64, also affords a good illustration of a 

 mammal from this formation. This genus is found in the middle Miocene, 

 as shown in the section, pag'e 7. 



The still more developed brain of the Pliocene mammals is seen in 

 figure 74, page 65, which gives a view of the skull of the Mastodon, with 

 the brain in position. In figure 76, page 65, the skull and brain of an 

 extinct Pliocene peccary further illustrates the same law of brain-growth. 



On comparing these various figures with those representing the brains 

 and skulls of the existing Ungulates, as shown by the succession in figures 

 77-83, on pages 66-67, the reader will have before him a series of facts 

 which illustrate the laws of brain-growth given on page 58. The 

 comj)arison, here confined to the representative ungulate mammals, might 

 easily be extended much farther, but Avould not come within the scope 

 of the present volume. 



The author has made similar comparisons in other groups of mammals, 

 including those that can be followed from the early Tertiary to the present 

 time, and the results are uniformly the same. These results the author 

 hopes to present fully elsewhere at no distant day. 



