GENERAL ORNITHOLOGY 



hsemal spines of vertebrae. Though such morphological character 

 is appreciable in those animals which have a long jointed sternum, 

 the segments of which, answering to pairs of ribs, develop from 

 separate centres, there is little or nothing in the development or 

 physical characters of the avian sternum to favour this view. The 

 great bone floors the chest and more or less of the belly, and fur- 

 nishes the main 'goiid d'appui of both the bony and muscular 

 apparatus of flight, receiving important bones of the scapular arch 

 and giving origin to the immense pectoral muscles. (See also Fig. 

 58.) 



Birds ofier two leading types of sternal structure, the ratite and 

 the carinate, or the "raft-like" and the "boat-like," according as 

 the bone is flat or keeled (Lat. ratis, a raft; adj. ratite/ in an arbi- 

 trary nom. pi., BatitcB, a name of one of the leading divisions of 

 birds : Lat. carina, a keel ; adj. carinate : nom. pi. Garinatce, name 

 of another such division). 1. In all struthious birds, comprehend- 

 ing the ostrich and its allies (and also in the Cretaceous Hesperornis), 

 the sternum is a flattish, or rather concavo-convex, buckler-like bone, 

 of somewhat squarish or rhomboidal shape, developed from a single 

 pair of lateral centres of ossification — a "flat-boat," without any 

 keel, built with reference to an important modification of the 

 shoulder-girdle, and a reduced or rudimentary condition of the 

 wings, which are unfit for flight. 2. In all flying birds, and some 

 which from other than any fault of the sternum do not fly — com- 

 prising all remaining recent birds, or Carinatce, and also the Creta- 

 ceous Ichthyornis — the sternum is keeled and develops from a 

 median centre of ossification as well as from lateral paired centres ; 

 usually two of these, making five in all. In a few Carinatce the 

 keel is rudimentary, as the flightless ground parrot of New Zealand, 

 Stringops habroptilus ; or otherwise anomalous, as in the extra- 

 ordinary Opistfwcomus cristatus, where it is cut away in front, and 

 in the rail-like Notornis, where the sternum is extremely like a 

 lizard's. In general, the development of the ked is an index of 

 wing-power, whether for flying or swimming, or both ; the eifective- 

 ness of the pectoral muscles being rather in proportion to depth 

 of keel than to extent of the sides of the "boat-bone"; thus, 

 the keel is enormous in swifts {Cypselidm) and humming-birds 

 (Trochilidm). 



The carinate sternum normally develops from five centres, 

 having consequently as many separate pieces in early life. Two of 

 these are lateral and in pairs ; the third is median and single. The 

 median ossification, which includes the keel, is the lophostem (Gr. 

 \6<j>os, lophos, a crest ; do-rtov, osteon, a bone). The anterior lateral 

 piece, that with which the ribs, or some of them, articulate, is the 

 pelurosteon (Gr. irXivpov, pleurm, a rib) ; in adult life this becomes 



