214 



GENERAL ORNITHOLOGY 



PART II 



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

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

 the lophosteon is extremely narrow, and fissured deeply away from 

 the metostea, 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 dromaBO- 

 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 pair 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 Bicho- 

 lophus a posterior median cartilaginous 

 flap having a separate centre, named 

 wosteon (Gr. ovpa, oura, 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 manubrium (Lat. mamuhriwm, 

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

 passerine well marked in Passerine birds (Fig. 58) ; 



Fig. 6S. — Typical 

 sternum, pectoral arches, and ster- ■, i.i_t l i^i i j 



nai ends of ribs ; from the robin, and may be Diiurcate at the end. and run 



down the front of the keel some way, as 



the raven. The fore border of the 



Tv/rdus migratorius, nat. size ; Dr^ 

 E. W. Shufeldt, U.S.A. Sternum 

 single - notched, with prominent 

 costal processes and forked manu- 

 brium ; five ribs reaching sternum, 

 one rib " floating." 



in tne raven. 



sternum is generally greatly convex from 

 side to side, and then, in those birds which 

 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 way. 

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

 a series of articular facets for the ribs, which 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. '\ 



