Mammalia: Nervous System 



703 



It is not mere bulk of brain that counts. It is the number of nervous 

 elements, greater number making possible a greater number and 

 variety of nervous correlations and adjustments and, accordingly, a 

 more complex pattern of behavior. 



Brains of monotremes and many other "low" mammals are, in 

 external form, not conspicuously unlike brains of reptiles. But brains of 

 ungulates, carnivores, and primates differ from reptilian brains in 

 external appearance so markedly as to make it seem hardly possible 

 that there is not some basic difference in plan of structure (Fig. 521). 

 The relatively greater size of the mammalian brain is a consequence of 

 increased number of neurons, but the added cells have not been uni- 

 formly distributed throughout all parts of the brain. Therefore its 

 proportions are changed. It is chiefly in one region, the telencephalon, 

 that this change has occurred. 



It was Ludwig Edinger, a neurologist of the latter part of the 

 nineteenth century, who made a distinction between the "old brain" 

 and the "new brain" of vertebrates. In fishes the five regions charac- 



Fig. 521. Brains of (4) alligator, (B) rabbit, and (C) dog. Dorsal views. (B.oi, 

 in .4) Olfactory bulb at anterior end of olfactory peduncle (/); (B.oi, in B and C) 

 olfactory lobe; (Fi.p) pallial fissure; (G.p.) pineal body; {HH, in 4) cerebellum; 

 (////, HH 1 , in B and C) lateral lobes of cerebellum; {Med) spinal cord; (MH) optic 

 lobes; (NH) medulla oblongata; (VH) cerebral hemispheres; (Wu) median vermis 

 of cerebellum; (ZH) diencephalon; (V-XI) cranial nerves; (1, 2) first and second 

 spinal nerves. (Courtesy, Wiedersheim: "Grundriss der veigleichendeu Anatomie 

 der Wirbeltiere," Jena, (lustav Fischer.) 



