GENERAL ZOOLOGY 



Nasal cavity 

 Olfactory nerve (I) 



Optic nerve (II) 



Optic chiasma 

 Hypophysis 



Auditory nerve (VIII) 

 Medulla 



Spinal cord 



Ramus communicans 



Sympathetic trunk 

 Sympathetic ganglion 



Cranial 

 nerves 



fig. 4.2. Nervous system of the frog, from ventral view. (Redrawn from R. Wiedersheim, 

 Comparative Anatomy oj Vertebrates, copyright 1907 by The Macmillan Co., printed by 

 permission. ) 



and the metencephalon, characterize different classes of vertebrates. The 

 cerebral hemispheres develop from the dorsal part of the telencephalon, and 

 the cerebellum arises from the dorsal part of the metencephalon. Figure 4.1 

 shows the relative development of cerebral hemispheres and cerebellum in 

 different vertebrates. It will be noticed that the brain of man seems to be 

 composed of only cerebral hemispheres, because they have overgrown the 

 other parts of the brain (see Fig. 3.1, p. 46). 



One of the distinguishing characteristics of the phylum Chordata, to which 

 the vertebrates belong, is the presence of a dorsal, tubular, central nervous 

 system. The brain and spinal cord of vertebrates contain a continuous cavity, 

 which is expanded to form the ventricles of certain regions of the brain and 

 is reduced to the microscopic central canal in the spinal cord. The anterior 

 and posterior choroid plexuses are composed of the thin roofs of the diencephalon 



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