PHYLUM CHORDATA 



425 



synovial joints. Ossified uncinates are nearly always present, and 

 usually become ankylosed to the vertebral ribs. 



What may be considered as the normal type of sternum, is a 

 broad plate, concave dorsally from side to side, and produced 

 ventrally into an antero-posterior keel which is ossified from a 

 distinct centre (Fig. 1062, A, os. 1). The posterior edge of the bone 

 is either entire (D), or presents on each side of the keel one or two 

 more or less deep notches (A, B) or foramina (C). In the Ratitoe 



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Fig. 1062, — sterna of various Birds. A, Gallus (common Fowl, young) ; B, Turdus (Tlirush) ; 

 0, VuUur (Viilture) ; D, Frocellaria (Petrel) ; E, Casuarius (Cassowary), unt. hit. in: 

 anterior lateral process ; car. carina ; H. clavicle ; cor. coracoid ; jbn. fontanelle ; fur. furcula ; 

 obi. lat.py. oblique lateral process ; os. paired ossification of sternum in E ; o«. i. carina! ossifi- 

 cation in A; 08.^, OS. 3, lateral ossifications; 'post.mcd.yiv. posterior median i)rocess ; 

 ;K>8i. iai. pr. posterior lateral process ; pr.cov. pro-coracoid ; scp. scapula ; sp. spina stern i. 

 (A and E after W. K, Parker ; B, 0, and D, from Bronn's 'J hierreicli.) 



(E) the keel is either absent or reduced to the merest vestige, and 

 there is no trace of the carinal ossification in the young. External 

 to the coracoid grooves, the anterior edge of the sternum is pro- 

 duced into larger or smaller antero-lateral processes (ant. led. pr.) ; 

 in the Emu these are of great size and are closely applied to the 

 pericardium. 



It was upon the characters of the raft-like sternum that the 

 group Ratitae was founded ; but the difference between them and 

 the Carinatse in this respect is not absolute, the ratite condition 



