CLASSIFICATION OF BIRDS. 627 



system, " the umbilicus becomes completely closed, the allantois shrivels 

 up, and the chick, piercing the broad end of the shell with repeated 

 blows of its beak, steps out into the world. " 



Classification of Birds. 



I. Sub-Class Arch^eornithes or Saurur^e. Ancient extinct birds, 

 connecting Birds and Reptiles. 



The oldest known bird is Archceopteryx, two specimens of which 

 have been found in the Solenhofen slates in the Upper Oolite (Jurassic) 

 of Bavaria. "The stone is so fine grained, that, besides the bones of 

 the wings, the furculum or merrythought, the pelvis, the legs, and the 

 tail, we have actually casts or impressions on the stone (made when it 

 was as yet only soft mud) of all the feathers of the wings, and of the 

 tail." — (Nicholson and Lydekker.) 



This link between Birds and Reptiles seems to have been a land bird 

 about the size of a crow. The upper jaw shows thirteen pairs of 

 conical teeth, the lower about three pairs. Each of the twenty 

 vertebrae of the long tail bears a pair of lateral rectrices — a unique 

 arrangement. There is no pygostyle. The vertebras have flat ends ; 

 the ribs are very slender, without uncinate processes ; there seem to 

 have been "abdominal ribs"; the sternum is not known. There are 

 separate metacarpals ; the first finger has two phalanges, the second 

 three, the third three or four, and all are clawed. There is a tarso- 

 metatarsus and four toes, as in the pigeon. 



II. Sub-Class Neornithes. 

 The metacarpals are fused. The second finger is the longest, and 

 the third is reduced. Only in Opisthocotnus are the three digits of the 

 fore-limb clawed ; in most cases claws are confined to the thumbs. 

 Caudal vertebrae are apparently not more than thirteen in numbei. 

 There is usually a pygostyle. 



1. Division Rati'm:. Running Birds with raft-like unkeeled \ 

 breast-bone. 



The African Ostrich (Struthio) is represented by two or three species, 

 at home in the plains and deserts of Africa, and notable for their size, 

 swiftness of foot, and beauty. There are but two toes, the third and 

 the fourth, with stunted nails. There are no clavicles. The pubes 

 form a ventral symphysis. The enormous size of rectum and caeca is a 

 unique character. The ostrich is polygamous, and at the breeding 

 season the hens lay the eggs, at intervals, in a hollow dug out in the 

 sand by the male. The eggs are incubated by the parents alternately, 

 the male sitting during the night, but in the hottest regions they are 

 sometimes left during part of the day simply covered by the sand. 



The American Ostrich (Rhea is represented by three species in the 

 S. American Pampas. In the Rhea there are three toes, all clawed, 

 and the ischia form a ventral symphysis. There are no clavicles. 

 Only here among Ratitae is there a well-developed syrinx. The caeca 

 are large. The male excavates a shallow nest in the ground, and 

 there, surrounded by a few leaves and grasses, the numerous eggs are 



