THE PIGEON 189 



highly developed here? Find the pineal body (in the angle 

 between and behind the hemispheres) , the optic lobes, the 

 olfactory lobes and the medulla oblongata. What are the 

 uses of each? 



Draw dorsal view (X2). 



(3) Cut the brain along the cavity between the hemi- 

 spheres, thus exposing the right and left halves. How 

 many cavities do you find? The front one is the third ven- 

 tricle, the next the Sylvian aqueduct, and the last, the 

 fourth ventricle. 



Draw left half (X2). 



(4) Trace the nerve to the eye. What do you find when 

 you trace it back to the brain? This crossing is the optic 

 chiasma. Remove part of the bone from around the eye 

 socket. Note the lining of the eye and the eyelids. Are 

 the eyelids movable? Are they both movable to the same 

 degree? Break away the bone until the muscles are ex- 

 posed. How many pairs of muscles? Can you find the 

 muscle of the nictitating membrane? 



Dissect the eye. Do you find the parts of a perfect eye? 

 Describe each of the parts. What is the difference between 

 the iris of the fish and that of the bird? Can birds see 

 as well in the night as in the day? What structure of the 

 eye enables some birds to see better at night than others? 



(5) Note the roots of the cranial nerves as they leave the 

 brain for different parts of the head. Do the places to 

 which they go suggest their function? Do you find nerves 

 leading off from the medulla oblongata and the spinal cord ? 

 What are they called? 



Conscious or Unconscious Activity. — (a) The or- 

 ganization of the nervous system of the pigeon, consisting 



