XXII. 2 



586 BATS 



of skin, involving all the digits of the hand except the first, and 

 extending also along the sides of the body to include the legs (but not 

 the feet) and, usually, the tail. The chief skeletal modification is there- 

 fore a great elongation of the arm, and especially of its more distal 

 bones (Fig. 365). The sternum carries a keel for the attachment of the 



Fig. 365. Skeleton of fruit bat (Pteropus). 



cl. clavicle;/, femur; fib. fibula; //. humerus; il. ilium; isc. ischium; pub. pubis; r. radius; 

 sc. scapula; st. sternum; tib. tibia; u. ulna. (From Reynolds, The Vertebrate Skeleton, after 



Shipley and MacBride.) 



large pectoral muscles and the clavicle is stout, often fused with the 

 sternum and with the scapula. Since the thorax is used as a fixation 

 point for the flight muscles the ribs move relatively little on each other 

 and respiration is mainly by the diaphragm. The ribs are flattened and 

 may indeed be fused together and with the vertebrae. The charac- 

 teristics of the arms and thorax are rather similar in these flying 

 animals to those found in brachiating arboreal creatures, such as 

 gibbons, which also have long arms and large, fixed thoracic cages. 

 The humerus is very long and carries a large greater tuberosity, 

 which may acquire a special articulation with the scapula. The 



