9IO STERNUM 



saving that the partition is traversed by the trachea and (ESOPHAGUS. 

 The s'pina sternalis is not, as often stated, the homologue of the 

 manubrium sterni of Mammals, for that is equivalent to the right and 

 left anterior lateral processes.^ It is to be understood that so far 

 all these structures are cartilaginous. 



Ossification of the Sternum does not begin till after it has 

 attained its final shape, and proceeds from various centres, which, 

 notwithstanding the elaborate studies of GeofFroy St. -Hilaire, 

 L'Herminier and Parker cannot always be recognized in the different 

 groups of Birds, chiefly owing to the variable situation of these 

 centres — one or another being suppressed and its place taken by 

 the extension of its neighbours. As a rule ossification begins 

 earliest where the greatest strength or resistance is needed. Thus 

 in Rhea, Gallinx, Turnix, Lestris and the Passeres, each anterior 

 lateral process has its pro-osteon (Parker), but in many other forms, 

 as Ardea, Rallidx and Ibis, these processes possess no special centre 

 of ossification, and are converted into bone by the extension of the 

 pleurosiea, Avhich last occur in the majority of Birds, though absent 

 in Turnix and the Gallinx, and lie in the lateral margin of the 

 Sternum, where the ribs are attached : coracostea occur sometimes 

 at the anterior end of the Sternum, near the articulation of the 

 Coracoids, and in some Birds metostea are the centres whence the 

 posterior lateral processes ossify, while the loplwsteon (Parker), which 

 may be single, multiple or paired, is the centre of ossification for 

 the keel. 



The Duck and the common Fowl may be cited in particular 

 illustration of this variability. In the former no trace of ossifica- 

 tion is visible before the bird is about 6 weeks old, when the 

 centres appear in the anterior lateral processes. By the end of 

 the 7th week ossification extends over the lateral rib -bearing 

 margin. A few days later it reaches the coracoidal portion, and in 

 the course of the following weeks numerous irregular patches of 



^ The synonymy of the various parts of the Avine Sternum being somewhat 

 perplexing, the following may be of some use : — 



Processus lateralis anterior —jjroc. costalis of various authors ; j)rosfe;via7 lateral, 



L'Herminier; proc. sterno - coracoideus or j>?-aJcos- 

 talis, Fiirbringer. 

 ,, ,, posterior = lateral xiphisternal process, Parker ; trabecida inter- 



inedia and tral. lateralis, Fiirbringer. 

 ,, obliquus = ;;?•«&. lateralis, Fiirbringer. 

 Metasternum = a;ip/«osfer7?wm of various authors; median xiphisternal process, 



Parker. 

 Spina sternalis = rosirm/i., wrongly called manuhriivm by many; epistermim, 

 Owen. 

 „ ,, externa, = manu{yrium, rostrum, episternal process, apojihyse sous- 



episternale or sup6rieure, inferior rostrum. 

 „ „ \ntevna. — a,popliyse soiisipistemale, svi^ei'iov rostvina. 



