| OCR Text |
Show 1885.] MISS B. LINDSAY ON THE AVIAN STERNUM. 715 PLATE XLII. Diagrams of STRUTIIIO. Fig. 1. Left half of shoulder-girdle of 4 days' embryo: c.,p.c, and sc. are separate h. has been somewhat displaced towards the left of the body in dissection. 2. Primitive muscular bands of 4 days' embryo, 8 in number. The dotted lines mark the position of the corresponding ribs as ascertained by dissection. Of the six sternal ribs of a later stage, the two anterior only are united, confirming Bathke'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.l.p. and the division of the rectus into two parts (r.m. broken, a.ndr.1. attached to 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. 5. Of 15 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. Of 21 days' embryo. The xiphoid end has been added to p.l.p.; a.l.p. Is fully elongated; 1. is the thin ligament uniting the coracoids and sternum. 7. Of 25 days' embryo. The 6th 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. 0/27 days' embryo. The 6th 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 Casuarius and Bhca, but not in Struthio. The cartilaginous m.s. and p.l.p. have been lost in maceration. (Eeduced.) C O PLATE XLIII. Fig. 1. Bhea: sternum of young bird, with unfused halves, x£. C O 2. Bhea: sternum of adult bird, with halves partly fused, X^. (In very old birds the halves are almost completely fused.) C O 3. Struthio: 4 days'embryo (Xl); 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 Gannet at same stage ( X 2^). 5. Struthio: 10 days' embryo (X 1); back view. "I 6. Struthio : 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 wing, and the head and neck. 7. Struthio: 15 days' embryo (xl); showing spread of the feather-tracts and establishment of the scales on the foot. 8. Larus : 5 days' embryo (X 5) : left shoulder-girdle (ventral side), showing struthionic character of coracoid ; c£=clav.; ^>.c.=precor.; y=supplementary tissue of the coracoid ; x=separate centre for median furcular apophysis. 9, 10. Larus: 15 days' embryo ; posterior border of sternum ( X1), 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 precoracoid. PLATE XLIV. Fig. 1. Coracoid of Diomedea exulans. Showing p.c.= precoracoid of Sabatier; cor.ep. epiphysis of the coracoid (Parker's precoracoid); p.p.c. = posterior process of the coracoid ; a. paired anterior apophysis of the sternum. CO. |
