350 



COLLEGE ZOOLOGY 



THE NAME, ORIGIN, INSERTION, AND ACTION OF SOME OF THE 

 MUSCLES OF THE HINDLIMB OF THE FROG 



Nervous system 



The principal function of the nervous 

 system is coordination of parts of the body 

 that are widely separated. 



The nervous svstem of vertebrates is more 

 complex than that of any other animals. 

 It is composed of two main subdivisions: 

 (1) a central nervous system consisting of 

 the brain and spinal cord and (2) a 

 peripheral ner\'ous system includes the cere- 

 bral and spinal nerves together with the 

 automatic system. The brain is protected by 

 the cranium of the skull. The brain consists 

 of 6 main parts when viewed dorsally (Fig. 

 234): (1) two olfactory lobes with nerves 



to the nostrils; (2) two cerebral hemis- 

 pheres; (3) diencephalon (between-brain) 

 which has a dorsal pineal body (epiphysis); 

 (4) two optic lobes; (5) cerebellum, a nar- 

 row transverse portion of the brain; and (6) 

 medulla (medulla oblongata) which joins 

 the spinal cord. 



On the ventral side of the diencephalon 

 the optic nerves cross each other to form the 

 optic chiasma. Just posterior to the optic 

 chiasma is the infundibulum, a large median 

 projection. The pituitary gland (hypophy- 

 sis) is the flattened ventral end of the in- 

 fundibulum. 



The cavities within the brain are shown 

 in Fig. 234. The cavities of both the brain 



