ANATOMY AND SUBDIVISION OF NERVOUS SYSTEM 123 



"face brain" (general cutaneous area), and "visceral brain" (vis- 

 ceral area) are all contained in the rhombencephalon, whose seg- 

 mental or stem portion is made up of these centers and the 

 corresponding motor centers. The same relations hold in the 

 human brain, and in both cases the cerebellum (and in man the 

 pons in the narrower sense in which I use that term) is added as 

 a suprasegmental part. In both cases the "eye brain" includes 

 the retina of the eye, the optic nerve, and a part of the roof of 

 the midbrain. In the fish a very small part of the thalamus 

 (not indicated on Figs. 43 and 44) also receives fibers from the 

 optic nerve. In man this optic part of the thalamus is greatly 

 enlarged, forming so large a part of that structure in fact that 

 the thalamus as a whole is often called the optic thalamus. It 

 should be remembered, however, that even in man the optic 

 centers comprise only a part of the thalamus. The "nose brain" 

 of the fish comprises most of the cerebral hemispheres (all except 

 the small "somatic area" of Fig. 44), and all of the epithalamus 

 and hypothalamus. In man these parts remain essentially un- 

 changed, but the "somatic area" of the hemisphere has greatly 

 enlarged to form the large corpus striatum and the enormous 

 cerebral cortex, the latter forming the suprasegmental apparatus 

 of the telencephalon, and greatly modifying the form relations 

 of all adjacent parts. 



The details of the development of the brain lie outside the 

 scope of this work, as also do the anthropological questions grow- 

 ing out of the statistical study of brain weights 1 and measure- 

 ments. These and many other topics of fundamental impor- 

 tance are presented in a very interesting way in Donaldson's 

 book on The Growth of the Brain. 



Summary. In all vertebrates the central nervous system is 

 fundamentally a hollow dorsal tube in which the primary seg- 

 mentation is subordinated to the development of important 

 longitudinal correlation tracts and centers. This tube is en- 

 larged at the front end to form the brain. The vertebrate brain 

 may be divided on physiological grounds into great divisions, 



1 The weight of the brain is exceedingly variable, even in a homogeneous 

 population. The average weight of the normal adult European male brain 

 is commonly stated to be 1360 grams (48 oz.), and that of the female 1250 

 grams (44 oz.). 



