A MANUAL OF ZOOLOGY 41 



THE NERVOUS SYSTEM AND THE OrtGANS OF 

 SPECIAL SENSE — The central nervous system consists 

 of the brain and the spinal cohd. Open the dorsal part 

 of the skull, cutting and picking away the cartilage of 

 which it is composed with the scissors and forceps until 

 the brain is ehtirely uncased. This will necessitate care- 

 ful work, especially where the olfactor/ lobes are continued 

 forward; the pituitary body downward, and the pineal body 

 upward. Cut the cranial nerves as far from their attach- 

 ment as possible. Are there sututes in the skull? When 

 you are picking away the skull investigate the structure, 

 first of the nostrils. Where do they open posteriorly? 

 Are they functional as organs of smell? .Second, the 

 structure of the eye. Note the muscles. How many pairs 

 are there? Are they fastened to the thick outer coat or 

 sclerotic? In what direction does each move the eye? 

 Take the eye from the socket cutting the optic nerve 

 close to the eye ball. Open the eye. What is the comr 

 parative shape of the lens? Is it different from the shape 

 of the lens in the higher forms? What is your conclusion 

 from the shape as jo the range of vision? Divide the two 

 lenses. What is the comparative size of the space filled 

 with the vitreous humor? Note the black inner coat, the 

 choroid, and interior to this the retrna. Does the optic 

 nerve enter the posterior part of the eye? Posterior to 

 the eye Carefully dissect out the mucous sac constituting 

 the ear. Does -it have a connection with the pharynx? 

 With the external surface? With the brain? Find the 

 ossicles. Test with HCl. What is their composition? Ose? 

 Trace the auditory nerve. What are the essential condi- 

 tions of hearing? Does it function as an organ of hearing? 

 What other function beside hearing has the ear in the 

 higher forms? Work out the muscles, using the, frog for 

 comparison. 



Find the olfactory lobes a^ the foremost part Of ,the 

 brain. Note the connection with the sensory membrane 

 of the nostrils. The short stem connecting these with the 

 body of the. brain is the olfactory tract. It is connected 

 with, the prosencephalon, a part of the fore-brain. On the 

 dorsal side, back of the fore-brain, constituting a paft of 

 the 'twixtbrain, note an upward and forward tube-Uke 



