OSSEOUS SYSTEM OF AVES. 19 



are directed upA\ ard and backward, usually overlapping the suc- 

 ceeding rib. In the Apteryx they occur in the second to the 

 eighth pair of ribs inclusive, and are articulated by a broad base 

 to a fissure in the hind border a little below the middle of the 

 rib : those belonging to the third — sixth ribs are the largest and 

 overlap. The articulations of the appendages persist in other 

 wingless birds, including the Penguins and Auks ; also in some 

 birds of flight : the RajJtores well exemplify the coalescence of the 

 appendage Avith its rib. The appendages to some of the ribs in 

 Picus are broader than they are long : the length much exceeds 

 the breadth in some Natatores ( Uria, Larus) and Grallatores 

 (^Hcematojms , PhoenicojHerus, jjI. 14). 



The moveable hsemapophyses, or sternal ribs, usually begin at 

 the third, sometimes the second, rarely, as in the Emeu, at the 

 fourth pair, more rarely, as in the Cassowary, at the fifth pair, of 

 the moveable pleurapophyses ; a pair of sternal ribs may also 

 exist answerino' to the seo-ment succeedino- the last of those which 

 have the long and moveable vertebral ribs ( Vultur\ The 

 common number of such htemapophyses is six pairs, of which the 

 first five articulate with the sternum ; the last usually having its 

 sternal end attached to the antecedent one. The lia3mapophyses 

 are longest, most slender and most numerous in the Guillemots 

 and Auks. There are eight pairs in Phalerus, Temm. ; seven 

 pairs in Uria. In Rhea and Dinornis elephantopus but three pairs 

 of haimapophyses articulate Avith the sternum. The sternal ribs 

 progressively increase in length from the first to the penultimate, 

 and converge towards the costal border of the sternum, where 

 they articulate with transverse elevations divided by narrow 

 depressions. Their upper end is but little, if at all, expanded, 

 and its articular surfiice is subconcave ; their lower or sternal end 

 is expanded from within outward, subcompressed from before 

 backward, and here is usually found the pneumatic foramen. In 

 the ostrich the sternal end supports two distinct articular surfaces, 

 each ha\dng its own capsular and synoA^al articulation with part 

 of the costal eminence.^ The joint between the pleur- and ha^m- 

 apophyses is also synovial and capsular. This is the main centre 

 upon which the respiratory movements hinge, the angles between 

 the vertebral and sternal ribs and between these and the sternum, 

 becoming more open in inspiration when the sternum is de- 

 pressed, and the contrary when the sternum is approximated to the 

 dorsal region in expiration. In some birds, chiefly of the terres- 

 trial or aquatic kinds, the vertebral and sternal portions of one or 



' XX-. i. p. 54, no, 254. 

 O 2 



