340 



PRACTICAL ZOOLOGY 



curved claws for capturing their prey. Birds that spend most 

 of their time in flight, like the swift, possess weak feet. Usually 



MO MP 



P P. M K 



FIG. 217. Anatomy of the pigeon 



A, nostril; AD, ad-digital primary feather; B, external auditory meatus; 

 BW, bastard wing ; C, oesophagus ; CA, right carotid artery ; D, crop ; DA, 

 aorta; E, keel of sternum; F, right auricle; G, right ventricle; HV, hepatic 

 vein; HI, left bile-duct; H2, right bile-duct; I, distal end of stomach; IA, 

 right innominate artery ; IV, posterior vena cava ; JA, left innominate artery ; 

 JV, right jugular vein ; K, gizzard ; L, liver ; M, duodenum ; MD, mid-digital 

 primary feathers; MP, metacarpal primaries; Ml, preaxial metacarpal; 

 M2, middle metacarpal; M3, postaxial metacarpal; N, cloacal aperture; 

 Nl, preaxial digit ; O, bursa Fabricii ; Ol, proximal phalanx of middle digit ; 

 O2, distal phalanx of middle digit ; P, pancreas ; PA, right pectoral artery ; 

 PD, predigital primary ; PV, portal vein ; PI, first pancreatic duct ; P2, second 

 pancreatic duct; P3, third pancreatic duct; Q, pygostyle; R, rectum; RC, 

 radial carpal bone ; RX, rectrices ; Rl, ulnar digit ; S, ureter ; SA ; right sub- 

 clavian artery; SV, right anterior vena cava; T, rectal diverticulum ; U, 

 kidney ; UC, ulnar carpal bone ; V, pelvis ; W, lung ; X, humerus ; Y, radius ; 

 Z, ulna. (From Marshall and Hurst.) 



there is one toe behind and three in front, but in many wood- 

 peckers there are two in front and two behind, an arrangement 

 which doubtless enables them to cling to the bark of trees more 



