136 GENERAL BIOLOGY 



U. External Anatomy. 



1 . Fins. How many are there ? Where are they located ? 

 Are they alike? Fins are said to be paired or single. The 

 paired are called pectoral, occupying a position similar to 

 the fore legs of the frog, and ventral, situated back of the 

 pectorals and on the ventral side of the body. How many 

 unpaired fins? The one just behind the vent is known 

 as the anal, one occupying the median dorsal position is 

 the dorsal. What others are present and how characterized ? 

 Study especially the structure of the paired fins and com- 

 pare with the others. In what alike, in what different? 

 Study also the ray-like structure of the supporting rods 

 of the fins, are they alike in all? 



2. Mouth. Note its shape and size. Open and close 

 the lower jaw and observe the movements of the several 

 parts. Are there lips? Identify the following bones of 

 the upper jaw: premaxillary, forming the anterior and lateral 

 portion and extending backward to unite with the maxillary. 

 Do both bear teeth? What is the shape of the teeth? The 

 lower jaw is composed of the dentary bones. Do they bear 

 teeth? Compare with those of the upper jaw. Within 

 the mouth cavity note the shape, size and position of the 

 tongue. 



3. The Eyes. Observe their location, size and shape. 

 Test the range of motion by pressing them with the forceps 

 or finger . Are there eyelids ? 



4. Nostrils. How many openings? What is their shape 

 and position? Do the nostrils communicate with the 

 mouth as in the frog? Are they of use in breathing? How 

 do they operate in smelling? 



5. Gill Openings. Observe that these openings are on 

 the side of the head and are covered by flaps, the opercles. 



