Subject headings are words and phrases which constitute a "controlled vocabulary" to categorize books by subject field. Subject headings often indicate the contents of books in terms that their titles (or your keywords) do not use, which often may be very general.
Use general subject headings for searching a broad topic or more specific subject headings for a specific author, historical period, or animal. You will find (more) headings specific to the subject category within the left-hand facets in the library catalog. If you want to see the subject headings for a specific title, click on the "details" link in the title record.
                    
        
            Encyclopedia of Evolution
        
                    
                by
            
        
        
            Mark Pagel
        
                    
        
                
                            
        
        
                    
                    
        
            The encyclopedia of farm animal nutrition
        
                    
                by
            
        
        
            M.F. Fuller
        
                    
        
                
                            
        
        
                    
                    
        
            The Continuum Encyclopedia of Animal Symbolism in Art
        
                    
                by
            
        
        
            Hope B. Werness