i6 



CASSELL'S BOOK OF BIRDS. 



their powers of flight. In the Swifts and the Humming-birds every bone of the skeleton, even to 

 the toes and the claws, is permeated by the atmospheric fluid. In the opposite extreme, the 

 terrestrial Apteryx and the aquatic Penguin have not a single bone thus excavated. 



The skeleton of an animal formed for flight must be constructed upon mechanical principles of a 

 very refined character. The utmost lightness is indispensable ; nevertheless, in a framework which 



Fig. 12. — SKELETON OF A BIRD. 



a, the Skull ; i, Vertebra of the Neck ; c, Dorsal Region of the Spine ; d, Vertebra that support the Tail ; e, e, e, the Sternum or Breast-bone : 

 /,/*/*/> tn e Ribs; h, the Scapula, or Shoulder-blade; *', i, the conjoined Clavicles or Collar-bones, forming the Furculum, or "Merry- 

 thought;" k, the Coracoid Bones ; /, the Humerus, or Arm-bone ; w, «, Bones of the Fore-arm; o,b\ Bones of the Wrist or Carpus ; 

 p, /, the Metacarpal Bones and Rudimentary Thumb ; g, q, Pieces representing the Middle Finger ; r, s, s, the Pelvis, formed by the 

 consolidation of the hinder Vertebra: of the Back into one piece ; t, the Thigh-bone ; u, the Leg ; x, x, the Tarso-Metatarsal Bones, usually 

 called the Tarsus ; y, the Hallux, or Hinder Toe ; j, z, the Front Toes. 



has to sustain the powerful action of muscles so vigorous, strength and firmness are equally essential. 

 It is in combining these two opposite qualities that the human mechanician exhibits the extent of his 

 resources and the accuracy of his knowledge ; but let the best and most ingenious mechanic carefully 

 examine the skeleton of a bird, and we doubt not that in its construction he will find all his ingenuity 

 surpassed, and perhaps derive not a little instruction from the survey. 



