THE FAUNA OF 



SOUTH AFRICA. 



AYES. 



BIEDS are warm-blooded vertebrate animals with an external 

 covering of feathers. They possess a four-chambered heart and a 

 complete double circulation, and have a single aortic arch on the 

 right side. The anterior pair of limbs are modified to form wings. 

 The bones of the skull join at an early period to form a continuous 

 brain-case which articulates with the vertebral column by a single 

 occipital condyle. The mandible or lower jaw articulates with the 

 skull on each side through the medium of a small bone, the quadrate. 

 The prcemaxilla and portions of the maxilla are prolonged anteriorly 

 and covered by a horny sheath to form the maxilla, upper mandible, 

 or superior half of the bill or beak ; the inandibular portion or lower 

 mandible is formed by a prolongation of the dentary bones of the 

 mandible. No existing birds have teeth, but many extinct forms 

 were well provided in this respect, and the germs are still to be 

 found in the embryonic Penguin. The bones of the great majority 

 of birds are to a large extent hollow, and capable of being filled with 

 warm air from the lungs through the medium of a series of inter- 

 vening air- sacs. All birds are oviparous. 



The one point which distinguishes birds from all other existing 

 animals is their covering of feathers. These are used as a means 

 of flight, as a protection to the body, or as ornaments. Excepting 

 in a few instances, as in the Penguins and Ostriches, the contour 

 or body feathers grow from certain definite tracts, called pterylce, 

 separated by intervening spaces, either bare or only covered with 

 down, but overlapped by the feathers on each side, and known as 

 apterice. The arrangement and extent of the feathered tracts varies 

 in different groups of birds and is of considerable importance in 

 indicating their affinities. 

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