400 STEEXUM OF THE PUFFIN PETREL. 



and the scapular form a very perfect ellipse, extend- 

 ing to about three-fourths of an entire circumference. 



Puffin Petrel, half the size of nature. 



Though the sternal apparatus of all these birds 

 possesses great power, that power does not indicate 

 an equal capacity of flight in the whole. The differ- 

 ences as connected with flying are chiefly found in 

 the posterior edge ; and as we have them in birds 

 which have the rest of their sternal apparatus very 

 much ahke, and have the habit of flying connected 

 with each, we are thereby better enabled to judge of 

 the difference between entire and partially divided 

 sternums than if we had the means of comparing 

 these only in birds which less resembled each other 

 in other respects. The diSerent species of storm 

 petrels which have the sternum entire, and conse- 

 quently the firmest origin for their pectoral muscles, 

 are among the most continued and excursive fliers 

 of which we have any knowledge. The wide sea is 

 their pasture, and, be its extent what it may, they 

 range from shore to shore ; now rushing at a mode- 



