VERTEBRATES 125 



Suggested drawings. 



a. The brain. 



b. The spinal cord and its nerves. 



c. The nervous system. 



d. A diagram of the cord and its nerves, showing the 

 kinds and the directions of the nerve impulses. 



The Endoskeleton of the Frog 

 Materials. 



Prepared frog skeletons mounted in glass-covered boxes 

 or in other cases suitable for individual study ; other ver- 

 tebrate skeletons for reference. 



Observations. 



The pupil should examine his specimen and identify the 

 following structures : — 



A. Skull: — 



1. Cranium, or brain case, the central and hinder portion. 



2. Nasal bone, a triangular bone lying in front of each 

 large opening, or eye orbit, and attached to the anterior 

 end of the cranium. 



3. Premaxillaries, a pair of small bones which form the 

 tip of the nose. 



4. Maxillary, a slender bone forming the side of the 

 upper jaw. 



5. Dentary, the bone of the lower jaw, corresponding to 

 the maxillary. 



. 6. Occipital foramen, the posterior opening or entrance 

 into the cranium, normally covered dorsally by cartilage 

 and most easily seen in a separate skull. 



B. Vertebral Column : — 



I. Cervical vertebra, the first vertebra, supporting the 

 skull. 



