1885.] MISS B. LINDSAY ON THE AVIAN STERNUM. 715 



Plate XLII. Diagrams of Struthio. 



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

 h. has been somewhat displaced towards tht; left of the body in dissection. 



2. Primitive muscular bands ofi days' emhryo, 8 in number. The dotted 

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

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

 are nnited, confirming Kathke'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. ^./). and the divisiim of 

 the rectus into two parts {r.m. broken, and r.l. attached io p.l.p.), united 

 by thinner and less differentiated muscular tissue. There are 6 sternal 

 ribs, and the two following are still long. 



4. Of 10 days' embryo : c. is attached, p.l.p. elongated. 



6. Of \b days e)nhryo. The halves of the sternum are united; m.«. and 

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



G. Of 21 days emhryo. The xiphoid end has been added io p.l.p. ; a.l.p. is 

 f idly elongated ; I. is the thin ligament uniting the coracoids and sternum. 



7. 0/2.5 days' emhryo. The fith sternal rib has lost its sternal attachment ; 

 but 7 a shows not only the Gth but also the nest rib still long on the 

 right side ; I, ligament. 



8. Of 21 days' emhryo. The Gth sternal rib having greatly shortened, the 

 adult condition is now attained, map])ed out in cartilage. 



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

 incompletely closed, a condition normal in Casuarius and Rhea, but not 

 in Struthio. The cartilaginous m.s. and p.l.p. have been lost in 

 maceration. (Reduced.) CO. 



Pl-Vte XLIII. 

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



2. Rhea: sternum of adult bird, with halves partly fused, X^. (In very 



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



3. Stritthio : 4 days' embryo ( X 1 ) ; showing length of tail and smallness 



of fore limb compared with chick of same age. 



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



digits. 4 a. Fore limb of Gaunet at same stage ( x 2^). 



5. Struthio: 10 days' embryo ( X 1); back view. "1 



6. iS'i;r2(;'^70 : 10 days' embryo ( X 1 ) ; side view. J 



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

 the dorsal surface, those of the ventral surface, of the thigh, the win", 

 and the head and neck. 



7. Struthio: 15 days' emhryo (xl); showing spread of the feather-tracts 



and establishment of the scales on the foot. 



8. Larus:^ 5 days' embrj-o (Xo): left shoulder-girdle (ventral side), 



showing struthionic character of coracoid ; c?. = clav. ; ^.c. = precor. ; 



^=supplementary tissue of the coracoid ; a?=separate centre for 



median furcular apophysis. 

 9, 10. Lanes : 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 bands in 



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



with the struthionic character of the preeoracoid. 



Plate XLIV. 

 Fig. 1. Coracoid ot Diomcdea exulans. Showing ^.c.= preeoracoid of Sabatier; 

 cor.ep. epiphysis of the coracoid (Parker's preeoracoid); p.p.c. = posterior 

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

 G.C. 



