GENERAL BIOLOGY 



of the brain posteriorly and contains the fourth ventricle which 

 is covered by a vascular part of the pia mater. 



c. CRANIAL NERVES. 



Ten pairs of nerves arise from the brain : 



1. Olfactory, a direct anterior continuation of the olfactory 

 lobe. 



2. Optic, also part of the original neural tube, arises from the 

 optic chiasma on the ventral side of the diencephalon. 



3. Oculomotor, arises from the ventral surface of the mesen- 

 cephalon just posterior to the optic chiasma; distributed to some 

 of the eye muscles. 



4. Patheticus, arises from the dorsal part of the brain just pos- 

 terior to the optic lobes ; distributed to one of the eye muscles. 



5. Trigeminal, arises from the side of the anterior part of the 

 medulla; distributed to the scalp, face and jaw. 



6. Abducens, arises near ventral fissure from anterior portion 

 of medulla; distributed to one eye muscle. 



7. Facial, arises from the side of the medulla near the origin 

 of the 5th with which it leaves the cranial cavity by a single orifice; 

 distributed to the facial area. 



8. Auditory, arises from the side of the medulla with the 7th; 

 sensory nerve to the ear. 



9. Glossopharyngeal, arises with the loth, just posterior to the 

 7th and 8th ; distributed to the tongue and pharynx. 



10. Vagus (pneumogastric), arises in conjunction with the 

 9th ; distributed to larynx, heart, stomach and lungs. 



d. SPINAL CORD OR MYELON. 



1. Forming the continuation of the medulla oblongata poste- 

 riorly, it rapidly tapers at about the fifth or sixth vertebra to form 

 a slender filament. On its dorsal surface is a median line, the 

 dorsal fissure. 



2. On each side ten spinal nerves arise from the cord. By care- 

 fully raising the cord a little, towards the posterior end, and search- 

 ing with a pocket lens, the nerves are seen to arise each by two 

 roots, one dorsal, one ventral. 



Make a sketch of the central nervous sytem and cranial nerves 

 as thus exposed. 



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