1885.] 



MISS B. LINDSAY ON THE AVIAN STERNUM. /I.') 



Plate XLII. Diagrams of Strutiho. 

 Fig. 1. Left half of shoulder-girdle of 4: days' embryo: c.,p.c., and so. are separate ; 

 h. has been somewhat displaced towards the left of the body in disseetiou.' 



2. Primitive inmcular hands of 4 days' embryo, 8 in number. The dotted 

 lines mark the position of the corresponding ribs as ascertained by dis- 

 section. Of the six sternal ribs of a later stage, the two anterior only 

 ai-6 nnited, confirming Eathke's statement as to the anterio posterior 

 coalescence of the primitive costal bands. 



Sterna (of natural size, excepting figs. 3 and 9). 



3. Of 7 days' embryo, seen from inside, m. is clearly shown, c. being not 

 yet attached, also the primitive condition of p.^.;/ aud the division of 

 the rectus into two parts {r.m. broken, and r.I. attached to^J./._?j.), united 

 by thinner and less differentiated nnis>:ular tissue. There are sternal 

 ribs, and the two following are still long. 



4. O/'IO days'^ eiuhryo : c. is attached, p.l.p. elongated. 



5. Of lo days embryo. The halves of the sternum are united; m.s. and 

 a.l.p. have been added, and the two posterior ribs shortened. 



6. 0/ 21 days' embryo. The xiphoid end has been added top.^'.p. ; a.l.p. is 

 ^ fully elongated ; I. is the thin hgament uniting the coracoids and sternum. 

 i . 0} 2o days' embryo. The (Ith sternal rib has lost its sternal attachment ■ 



but 7 a shows not only the 6th but also the next rib still long on the 

 right side ; I, ligament. 



8. 6^/27 days' embryo. The fith sternal rib having greatly shortened, the 

 adult condition is now attained, mapped out in cartilage. 



9. Of adult Ostrich : p.c. shows its occasional condition of atrophy ; m. is 

 incompletely closed, a condition normal in Castuirius and Rhoa, but not 

 m Struthio. The cartilaginous m.s. and »./.«. have been lost in 

 maceration. (Reduced.) CO. 



Plate XLIII. 

 Fig. 1. Hhea: sternum of young bird, with unfused halves, x^. CO. 



2. Bhea: sternum of adult bird, with halves iwrtly fused, xi. (In very 



old birds the halves are almost completely lused.) CO. 



3. <SVr;;^A/o : 4 days' embryo (xl); showing" length of tailand smallness 



ot lore limb compared with chick of same age. 



4. Struthio: 7 days' embryo ( x 1); showing division of fore limb into three 



digits. 4rt, Fore hmb of Gannet at same stage (X2A). 

 6. Struthio: 10 days' embryo (x 1): back view. "1 



6. Struthio : 10 days' embryo (x 1) ; side view. / 



Showing appearance of feather-tracts, five in number, viz. those of 

 the dorsal surface, those of the ventral surface, of the thio-h the wino- 

 and the head and neck. ' °' 



7. Struthio: \5Aay^ embryo (xl); shovring spread of the feather-tracts 



and establishment of the scales on the foot. 



8. Larus:_ 5 days' embryo (x5): left shoulder-gircUe (ventral side) 



showing struthionic character of coracoid ; c/. = clav. • « c =precor • 

 y=supplemeutary tissue of the coracoid ; ;r=separate centre for 

 median furcular apophysis. 



9. 10. Larus : 15 days' embryo ; posterior border of sternum ( x 1) showing 



processes. In 10 the two processes are united, a condition never seen 

 in any younger .stage. 

 11. Larus: 12 days' embryo, showing six sternal ribs and three bauds in 

 the rectus muscle, a struthionic condition, to be noted in connection 

 with the struthionic character of the preeoracoid. 



Plate XLIV. 

 Fig. 1. Coracoid of Diomedca exulans. Showing p.c. = preeoracoid of Sabatier • 

 cor.ep. eiJiphysis of the coracoid (Parker's preeoracoid); i'A«.c. = posterior 

 process of the coracoid ; a. paired anterior apophysis of the sternum. 



