VERTEBRATES 123 



Suggested drawings. 



a. The heart and lungs in their normal position. 



b. The circulatory system, as seen in the injected speci- 

 men. 



c. A copy of the diagram or model of the circulatory 

 system. 



d. A diagram of the respiratory tract from the nostrils 

 to the lungs, by arrows showing the course of the air. 



The Nervous System of the Frog 

 Materials. 



Specimens which have the brain exposed and other 

 specimens whose viscera have been removed so that the 

 spinal nerves can be seen ; pans or shallow dishes of water 

 and forceps. 



Observations. 



The nerve tissues are generally white in color unless 

 they have been specially treated and stained. The pupil 

 should identify the following structures : — 



A. Brain, those enlargements of nerve tissue situated 

 in the head and composed of four principal parts, as fol- 

 lows : — 



1 . Cerebral hemispheres, a pair of elongated lobes, the 

 anterior enlargements. 



2. Mid brain, or optic lobes, a pair of large ovoid struc- 

 tures, projecting diagonally forward and side wise. 



3. Cerebellum, a slender, transverse ridge, close behind 

 the midbrain. 



4. Medulla, the anterior end of the spinal cord, widest 

 in front and containing a triangular depression. 



(Frequently a pair of smaller enlargements is to be seen in front of 

 the cerebral hemispheres ; they are the olfactory lobes, and from them 

 nerves pass forward to the nasal chamber.) 



