84 INTRODUCTION TO ZOOLOGY. 



through the false diaphragm into the venous sinus. 

 Are there other veins entering? 



4. Find the arterial bulb in front of the ventricle. 

 Trace the branchial aorta from the arterial bulb until 

 it branches into the branchial arteries, one to each gill 

 arch. 



5. Trace one branchial artery along the gill arch 

 until it enters the dorsal aorta. 



6. Trace the dorsal aorta along the back as far as 

 you can. 



7. Is the heart single or double? Is it respiratory 

 or systemic? Describe the course of the blood from 

 the ventricle until it gets back to the ventricle again. 



The Jfervous System. 



1. Cut off the head, scrape away the flesh, and 

 slice off the top of the skull to see the brain. 



2. Notice the cellular tissue above the brain. 



3. The largest pair of lobes you see in the brain 

 are the optic lobes. 



4. In front of the optic lobes, find the pair of cer- 

 ebral hemispheres, or cerebrum. 



5. In front of the cerebrum, find two much smaller 

 lobes, the olfactory lobes. Trace the olfactory nerves 

 from the olfactory lobes forward. 



6. Behind the optic lobes, notice the undivided 

 cerebellum. 



7. Behind the cerebellum, find the medulla ob- 

 longata, which is continuous with the spinal cord. 



8. Find the optic nerves, below the cerebral and 

 olfactory lobes. Trace them to the eyes. Do they 

 unite? From which lobe does the nerve come that 

 goes to the right eye? 



9. Can you find small nerves (spinal nerves) 

 branching from the spinal cord? How far back does 

 the spinal cord extend? 



