i8 



The Anatomy of Birds 



is long, corresponding to the long bodies of these birds. The hinder portion of 

 the breast-bone may be entire, perforated, or notched, the notches being two or 

 four in number, reaching their extreme in the fowls in which the body of the ster- 

 num is very small and the lateral processes extremely long and slender. 



The front of the breast-bone (Fig. 13) may bear a projecting process, or 

 "manubrium," and this may be developed from the inner face of the bone, spina 

 internet, or outer, spina externa, at the region of the keel. The manubrium may 

 be a spine (Curassows), or low projection (some Owls), while the extreme develop- 

 ment is found in the long "Y "-shaped pro- 

 cess so characteristic of the Passeres, the ^feHT^ /t.f. 

 Woodpeckers coming next in this respect. 

 These characters are apparently not asso- 

 ciated with any corresponding modifications ^ >a ^" p '' p " 



FIG. 13. Sternum of Sage Grouse, show- 

 ing component bones. (After Shufeldt.) 



FIG. 14. Skull of Rhea, dorsal view. (After 

 Pycraft.) 



/./, temporal fossa; p.o.p., postorbital process; m.e, 

 mesethmoid; l.p, lachrymonasal pillar; /, lachrymal; 

 mxp.p, maxillopalatine; n, nasal. 



in the habits of birds, and are, therefore, of great importance in determining 

 the affinities of various groups. % 



On either side of the breast-bone are little prominences to which the ribs 

 articulate, and in many birds these articulations are found well forward and on 

 a triangular-shaped process, termed the costal process. 



The uppermost bone of the leg, the femur, is always short, even in wading 

 birds, and usually pneumatic, or permeated by air. The extreme of shortness 

 and width is found in the extinct diving bird Hesperornis, in which the femur 

 suggests that of a seal. 



The knee-pan, or patella, is usually small, except in such swimming birds as 

 Cormorants and the extinct Hesperornis, where the head of the tibia is short, and 

 it is largely developed to serve for the attachment of muscles. In Grebes and 

 Loons the upper end of the tibia is greatly extended and the knee-pan corre- 

 spondingly reduced, appearing as a small splint of bone back of the process. 



