X INTRODUCTION. 



The anterior extremities are composed as follows : 

 The clavicles unite to form the furcula or merry-thought 

 bone ; and are joined to the sternum by ligament or 

 cartilage. They are entirely wanting in some birds, as 

 in certain genera of Parrots, and in others are not joined, 

 and are very short. The coracoid apophyses, or coracoid 

 clavicles of some, which are always present, are at- 

 tached to the edge of the sternum, and, with the scapula, 

 form the articular surface for the head of the humerus. 

 The strength and width of the furcula, which serves to 

 keep the shoulders apart, in opposition to the strong force 

 exerted by the muscular action of the wings in flight, in 

 general corresponds with the power of flight of the bird ; 

 but Parrots are an exception, for their clavicles are flat and 

 comparatively weak. The fore-arm consists of the ulna and 

 radius, the latter thin and feeble. The hand is elongated, 

 and consists of two short carpal bones, two metacarpal 

 bones, one complete digit, and the rudiments of two others ; 

 besides the so-called thumb, a styliform process of two 

 phalanges. This, however, as in the case of the foot, does 

 not represent the true thumb, but the index finger ; and as 

 we found the true thumb of the foot sometimes represent- 

 ed by a spur, so is the true thumb of the hand occasion- 

 ally represented by a spur, as in some Plovers, Parra, 

 Plectropterus, and more especially in the Chauna chavaria 

 of South America. 



The leg bones consist of a short femur, always directed 

 forwards ; a long tibia, with an imperfect fibula anchylosed 

 to it ; a patella ; an anchylosed tarso-metatarsal bone (the 

 tarsus) ; and the toes, already treated of in the external 

 anatomy of the Bird. 



Arboreal birds, which perch and roost on trees, do so 

 without the exertion of anv muscular force. A suite of 



