214 



GENERAL ORNITHOLOGY 



occurs. The extreme case of eraarginatiou of the sternum is afforded 

 by the Gallince, and is highly characteristic of that group. Here 

 the lophosteon is extremely narrow, and fissured deeply away from 

 the nietostea, which latter are deeply forked ; the arrangement 

 giving rise to two very long slender lateral processes on each side 

 (Figs. 1 and 2, p. 73). The sternum of the tinamou, a drom?eo- 

 gnathous bird, is still more deeply emarginated, but the extremely 

 long and slender lateral processes, which enclose an oval contour, 

 are simple, not forked. 



In a very few birds there are centres of ossification additional 

 to those above described. In Turnix, there are said by Parker to 

 be a i^air of centres between the pleur- 

 ostea, which he names coracostea, because 

 related to the part of the sternum with 

 which the coracoids (see p. 216) unite. 

 The same authority describes for Dicho- 

 lophus a posterior median cartilaginous 

 flap having a separate centre, named 

 ur osteon (Gr. ovpa, our a, tail). In various 

 birds the sternum is eked out in the 

 middle line behind by cartilage which 

 has no ossification. 



The sternum, especially of the higher 

 birds, develops in the middle line in 

 front a beak - like process called the 

 rostrum or manuhrium (Lat. r^ianubrium, 

 a handle) ; its size and shape vary ; it is 

 Fig. 5s. — Typical passerine Avell marked in Passerine birds (Fig. 58); 



sternum, pectoral arches, and ster- i ^ ^ -r , , ,^ ^ ^ 



nai ends of ribs ; from the robin, and may be bif urcate at the end and run 

 R^wf s"J.at?u:s"A.- tti;-n?m- ^owu the front of the keel some way, as 

 single - notched, with prominent in the raven. The fore border of the 



costal processes and forl<ed manu- . ,, , . 



briiim; five ribs reaching sternum, stcmum IS generally greatly coiivcx irom 



one rib " floating." ^j^^ ^^ ^j^^^^ ,^^^ ^j^^^^^ • ^^ ^^^^^ ^^j^^^ ^j^j^j^ 



have prominent pleurostea, produced in angular costal processes. This 

 border is also thickened," and presents on each side a well-marked, 

 smooth-faced groove, in which the expanded feet of the coracoid bones 

 are instepped and firmly articulated. These deep grooves commonly 

 meet in the middle ; are occasionally continuous from one side to 

 the other ; sometimes each crosses to the other side a little Avay. 

 The costal processes on each side also have thickened edges, with 

 a series of articular facets for the ribs, Avhich gives this border a 

 fluted or serrate profile. Generally the fore half, or rather less, of 

 the side border of the sternum is thus articular ; and it is only such 

 costiferous (rib-bearing) extent of sternum which corresponds to the 

 whole body of the bone in a mammal, all the rest being "xiphoid." 



