716 MISS B. LINDSAY ON TH K AVIAN STERNUM. [Juiie IG, 



Fig. 2. Shoulder-girdle of late ."> days' chick, showing relations of c^. = clavicle 

 and eor. = coracoid. The coracoid has a flattened shape ; the scapula 

 is removed. 

 3. The same, in aifu. 



4 5. Shoulder-girdle of two 5 days' chicks (right and left). Showing clavicle 

 adjoined ti coracoid, scapula quite free ; ventral surface. Erratuiii: 

 R. and L. are reversed in the diags., and sc. is put for cl. in fig. 5. 



6. Six days' chick, showing (1) absence of interclavicle, (2) fused coraco- 



scapular plate, removed from position of dotted line, (.3) elongated 

 cla\icle ; also (4) rectus attached to cla\icle (</. fig. 9). 



7, 8. Ei>;ht coracoid of Casuarius, showing the foramen or iucisura cora- 



coidea, which in Sfnifkio lies near the inner margin of the cora?oid. 

 The nren internal to it is probably a precoracoid (not identical with that 

 of Struthio) ; cf, fig. 1, also woodcut diagram of shoulder-girdle of 

 Chick. C.C. 

 9. Uria iroile: 7 days' embryo, showing clavicles closed before the sternum 

 and giving attachment to rectus muscle, r. 



10. Vria troilc: about 15 d.ays': rl, external rectus continuous with pe.?to- 



ralis major ; r 2, main sheet of rectus ; r 3, internal thin sheet of rectus ; 

 s=supracoracoideus (or pect. minor). 



11. The same, showing attachment of r 3 on the dorsal side of the sternum. 



12. Tlie same, showing attachment of rS nearer the margin, at a later stage. 



13. 14. The same, ribs of 7 days' embryo ; 13 shows m', traces of the 



primitive intercostales evterni, dissected out. 



15. Dni/ixpiis, showing relations of clav., precor., and /, for. cor., in young 



bird. C.C. 



16. Coracoid of adult bird : /, foramen ; ff, posterior border of coracoid. 



C.C. 



Plate XLV. 



Fig. 1. Chick, 6-7 d.xys' incubation, showing rectus (r.) continuous with supra- 

 coracoideus (p. onin.); x2J;. 



2. Embryonic sternal ribs of late 6 days' chick, eleven in number, the early 



form of the posterior processes is also shown. 



3. LateCdays" chick, .showing;/*', primitive b^indsof the intercostales externi, 



and wedge-shaped ujiper part severed from rectus band b\- growth of 

 sternum — removed from X. Parts of the rectus=r. and r.^.; X4. 



4. .5. Occasional separate centre, Ic, for keel in 7 days' chick. 



6. The wedge shaped rectus band, together with (w') three anterior muscle- 



bands (primitive interco.stales externi). of late (> days' chick. 



7. The same at a rather later stage (very early 7 day.s' chick) ; x4. 



8. Last trace of the three anterior muscle-bands, in 7 days' chick ; x4. 



9. Xormal sternum of 6 days' chick, showing commencemeut of external 



process, and {f) thin region towards median line : cf. fig. 8. 



10. Abnormal sternum of 6 days' chick, showing a process of the sternum 

 anterior to the coracoid, four rudiments apparently of anttrior ribs, 

 and the muscle-bands belonging to each, turned over. 



11 Five days" chick, showing (.i) lateral bands of mu.scle attached to lower 

 jaw ; upon the complete closure of the pericardial oavitj- these unite to 

 form the median band seen in figs. 3, C, and 7. 



12. Sternum of 5 days' chick (broken by needle), showing masses of dif- 

 ferentiating mesoblast alternate with the ribs, possibly indicating a 

 complex series of costal centres in the .sternum comparable with what 

 Albrecht calls " hemisteruebrals " in mammals ; and four antei'ior ribs 

 attached to the vertebral column, the posterior ones free. 



13. Gannet, Stage 1. r = rectus muscle. 



14. Gannet, Stage 2. c.s., mass of sternum, showing depression for attach- 

 ' meut of coracoid; A' = keel ; »i' = three rudimentary muscle-bands; 



Ay. = thick folds of hypoblast of the throat, which afterwards form the 

 thyroid glands. 



15. Gannet, Stage 3 ; dorsal aspect. Z;=keel ; Z and Z' = ligaments. 



16. 17. Gannet, Stage 4. L, ligament. 



18. Posterior margin of sternum of bird j ust hatched (x 1). 





