IV. VERTEBRATA: MAMMALIA 



551 



Since the mammals in general are distinguished from other vertebrates 

 by their intelligence, the brain is characterized by the size of cerebrum and 

 cerebellum (iig. 600) . In contrast to birds and fishes, the cerebellum (7 V) 

 is differentiated into a median vermis and lateral cerebellar hemispheres. 

 In the cerebrum the frontal lobes of the pallium grow forwards over the 

 olfactory lobes, which consequently He farther and farther back on the 

 lower surface. The temporal lobes extend right and left over the optic 

 lobes and down to the floor of the cranium; the occipital lobes cover 

 successively the mid brain, cereljellum, and medulla oblongata. Since 

 there is a great range of intelligence in the mammals, the cerebra may 

 be arranged in an ascending series. In the monotremes, marsupials, 

 insectivora, and rodents (fig. 600, A) the olfactory lobes are visible in 



Fig. 600. — A, brain of rabbit (after Gegenbaur). B, of fish otter. C, of 

 pavian monkey (after Leuret and Gratiolet). I, cerebrum; III, optic lobes; IV, 

 cerebellum; V, medulla oblongata; lo, olfactory lobes. 



front, usually the mid brain behind (///). In the lemurs, carnivores 

 (B), and ungulates the olfactory lobes are nearly, the cerebellum partly, 

 covered. In man and the anthropoid apes (C), on remo\dng the roof 

 of the skull, only the two cerebral hemispheres are visible. 



Further, it is to be noted that in the first group the surface of the cere- 

 brum is smooth, while in the others the cortex is increased by infolding and 

 the formation of convolutions (gyri and sulci) which reach their greatest 

 complication in the anthropoid apes and in man. A consequence of the 

 increase in size of the brain is the great development of the connecting 

 nerve tracts, which become more and more prominent as parts of the 

 brain. Thus the two halves of the cerebrum are connected by two 

 transverse tracts, the corpus callosum and the fornix; two solid cords, the 

 crura cerebri, run back from the cerebrum to the other parts, while a 



