166 



COMPARATIVE ANATOMY 



the wings in good fliers being considerably longer than the legs, 

 which alone bear the entire weight of the body when on the 

 ground (Fig. 132). In Cursorial Birds (Ratitse), however, the wing 

 has undergone regressive changes in connection with their habits, 



ScJi. 



-MF 



- Z' 



FlG. 132. -SKELKTiiN OF THK LtMB.S AND TAIL OV A C'ARINATE BlKU. (The 



skeleton of the body is indicated by dotted lines.) 



F, digits ; Fl, fibula ; H W, carpus ; MF, tarsometatarsus ; MH, carpometa- 

 carpus ; OA, humerus ; OS, femur ; Py, pygostyle ; #, coracoid ; Rd, ulna ; 

 Sch, scapula ; >SV, sternum, with its keel (Cr) ; T, tibiotarsus ; //, radius ; 

 ~ ] , :., digits. 



and in the extinct New Zealand Moa (J)inornis) no trace of it 

 has been found : in Penguins it serves as a paddle. 



The relation of the superficial surface of the wings to the 

 weight of the body is far from constant, and depends largely on 

 the relative power of flight ; on the whole, the wings are relatively 

 largest in small, light Birds than in large, heavy ones. 



