194 BIOLOGY 



tough one called the dura mater, and a more delicate, inner 

 membrane, the pia mater. 



The Craniospinal Nerves. Twenty pairs of nerves arise 

 from the brain and cord, ten from the brain, and an equal 

 number from the cord. Those from the brain, the cranial 

 nerves, supply the organs of special sense and the muscles 

 and other organs of the head, the heart, lungs, and stomach. 

 They are as follows : 



1. The olfactory nerves, from the olfactory lobes supplying 

 the nasal cavities. 



2. The optic nerves. These two nerves arise from the optic 

 lobes, cross each other to form the optic chiasm, and then 

 each passes to the eye on the opposite side of the head. 



3. Motor ocularis, supplying the muscles of the eye. 



4. Patheticus, supplying the muscles of the eye. 



5. Trigeminal, supplying the sides of the head (sensory). 



6. Abducens, supplying the muscles of the eye. 



7. Facial, supplying the sides of the head (chiefly motor), 



8. Auditory, supplying the ear. 



9. Glossopharyngeal, supplying the pharynx and the tongue 

 (sensory). 



10. Pneumogastric, supplying the larynx, the heart, and the 

 stomach. 



From the spinal cord arise ten pairs of spinal nerves, one 

 between the skull and the first vertebra, and one between 

 each vertebra and the next; Fig. 95. The first supplies 

 the tongue (motor); the second and third unite to form the 

 nerve going to the arm, the brachial nerve (Lat. brachium = 

 arm); the fourth, fifth, and sixth supply the middle region 

 of the body; and the seventh, eighth, and ninth unite by cross 

 branches to form the sciatic plexus (Lat. plectare = to braid), 

 from which arise the, nerves that supply the leg, the sciatic 

 nerve, which is the largest in the body; the tenth nerve supplies 

 the region of the urostyle. Each nerve arises from the cord 

 by two roots, of which the anterior root carries impulses away 



