5 So 



MANUAL OF ZOOLOGY. 



angle is commonly united by ligament to the top of the ster- 

 num. The function of the clavicular or furcular arch is " to 

 oppose the forces which tend to press the humeri inwards 

 towards the mesial plane, during the downward stroke of the 

 wing " (Owen). Consequently the clavicles are stronger, and 

 their angle of union is more open, in proportion to the powers 

 of flight possessed by each bird. The furculum is rudimentary 

 in the Ostrich, Emeu, and Cassowary, and it is absent in the 

 Apteryx and some Parrots. 



We have next to consider the structure of the bones which 

 compose the fore-limb or " wing " of the bird ; and as this 



organ is the one which chief- 

 ly conditions the peculiar life 

 of the bird, it is in it that we 

 find some of the most charac- 

 teristic points of structure in 

 the whole skeleton. Though 

 considerably modified to suit 

 its function as an organ of 

 aerial progression, the wing 

 of the bird is readily seen to 

 be homologous with the arm 

 of a man or the fore-limb of 

 a Mammal (fig. 323, A, and 

 fig. 324). The upper arm 

 (brachiuiri) is supported by 

 a single bone, the humerus, 

 which is short and strong, 

 and articulates above with 

 the articular cavity formed 

 partly by the scapula and 

 partly by the coracoid (fig. 

 324, Ii). The humerus is 



ig. 324- Fore-limb of the Jar-falcon, h Succeeded dlStally by the 



Humerus ; r Radius ; u Ulna ; / "Thumb;" fore-arm (antlbrachlUm), COtt- 



m Metacarpals, anchylosed at their extrem- _ H ' fl -4._j v... f l. rr>rma1 Hvr 



ities;// Phalanges of fingers. StltUtCQ by the normal t\\O 



bones, the radius and ulna 



(fig. 324, r, u), of which the radius is the smaller and more 

 slender, and the ulna the larger and stronger. The ulna and 

 radius are followed inferiorly by the bones of the wrist or 

 carpus ; but these are reduced in number to two small bones, 

 one radial and one ulnar, " so wedged in between the anti- 

 brachium and metacarpus as to limit the motions of the hand 

 to those of abduction and adduction necessary for the folding 

 up and expansion of the wing ; the hand is thus fixed in a 



