LESSON 85.] 



NERVOUS SYSTEM IN BIEDS. 



273 



FIG. 388. 



FIG. 389. 



1227. The changes effected in the nervous system of the higher 

 amphibia closely resemble those produced by development in the 

 human embryo. Their sympathetic nerves, and ganglia, too, are 

 more distinct than in the class of fishes. 



1228. By comparing the nervous system of the adult Frog 

 (Fig. 388), with those of the tadpole during the period of early de- 

 velopment, great and important changes will be apparent. Thus, 

 the olfactory ganglia and nerves (nerves to the nose), which did not 

 at all appear before, are now well formed (a) ; the cerebal hemis- 

 pheres (b) are greatly enlarged, the optic lobes (c) well developed, 

 and the cerebellum (d) remains so small that it does not cover the 

 fourth ventricle, or cavity left by the divergence of the columns of 

 the spinal chord (e) ; the caucla 



equina (/,/) is also well produced 

 at the period of mature growth. 



1229. From the foregoing it 

 will be seen that the chief advance 

 in the development of the Reptile 

 brain, as compared with that of 

 Fishes, consists in the greatly in- 

 creased size of the cerebral hemis- 

 pheres over the optic lobes, but the 

 cerebellum is smaller so small in 

 the Frog that it does not even cov- 

 er the fourth ventricle, and this is 

 common to nearly the whole class. 



In confirmation of these facts a 

 figure is given of the brain of the 

 Turtle (Fig. 389); the olfactory 

 ganglia (a) are largely developed, 

 and form, with the eyes, the most important organs of special sense. 

 The cerebrum (b) is enormously produced, as compared either with 

 the optic ganglia (c), or the cerebellum (d). 



Nervous system 

 of adult Frog. 



Brain of the Turtle. 



LESSON LXXXY. 



NEKVOUS SYSTEM IN BIRDS. 



1230. In this class the cerebral hemispheres attain a great in- 

 crease of development, and arch backwards, so as partly to cover the 

 18 



