128 PRACTICAL ZOOLOGY. 



from the base of the brain will be seen the optic 

 nerves. Cut these close to the bone beneath. 



8. Back of the optic nerves are the small third and 

 fourth pairs of nerves, then the larger fifth, the small 

 sixth, and close together the seventh, the facial, and 

 eighth, the auditory, and farther back four more 

 pairs. Cut these all where they leave the brain-cav- 

 ity. 



If 9-17 are not to be done the same day, the spinal 

 cord may now be cut an inch back of the brain, and 

 the brain be put into alcohol for later study. 



9. Lay the rabbit on a narrow box, and let the head 

 hang over one end. Cut away as much as possible 

 of the muscle along the backbone. With the bone- 

 forceps unroof the whole length of the spinal cord in 

 the manner before described. 



10. Note carefully the variations in the diameter of the 

 spinal cord in its course. 



11. Observe the spinal nerves, passing off in pairs 

 through the spaces between the arches of the verte- 

 brae. Count the pairs of nerves, and compare them 

 in size in the different regions of the backbone. 



12. Carefully cut away the bone and other tissue around 

 some of the nerves in the region of the shoulder, and 

 make out that each spinal nerve has two roots, an 

 upper, in the natural position of the animal, and a 

 lower. These get their names from human anatomy, 

 the former being the posterior root, and the latter 

 the anterior root. Trace them to their union in the 

 one spinal nerve. 



13. On the posterior root, just before it joins the anterior, 

 find a swelling, the ganglion of the posterior root. 



