180 SHOULDER-GIRDLE AND BREAST-BONE. 



sword, and at its base the " acromion" is large and widely bifurcate. The coracoid has acquired 

 great slenderness of the shaft ; a more down-turned head ; a very rudimentary meso-coracoid 

 process ; a flat triangular posterior epicoracoid lobe ; and a hooked anterior lobe, the counterpart 

 of the distinct epicoracoid bone of the Monotreme. 



The Sternum has acquired a very large keel, and the front of the bone is divided by a broad 

 and rather shallow notch into two equal parts ; the lower belonging to the keel, and the upper to 

 the rostrum. This latter part is very large, looks more upwards than forwards, is strongly carinate 

 antero-inferiorly, is thick and round above, towards, and along its strong forks, and scooped 

 below, where its base becomes coincident with the lower coracoid lip. The upper lips form part 

 of a strong, low, transverse wall, running from one costal process to the other ; these latter 

 processes have become sharper, longer, and more forthstanding. The xiphoid notch (one on each 

 side) is half the length of the Sternum ; it is triangular, and very large : the external xiphoid 

 process is long, very narrow, pedate ; and does not diverge so much as in the embryo. The body 

 of the Sternum is angularly deep ; the middle xiphoid plate has its notch filled up, and its pos- 

 terior margin slightly arcuate, and developed into eared corners, tending to bound-in the notch. 

 On the right side of the anterior part of the great notch there are (in the specimen before me) 

 two small fenestrse; these show a disposition to a further fissure of the Sternum, and are seen in 

 many of the lYingillinse, and in other Passerines. There are five costal condyles on each 

 side ; the Sternum, like the other bones, except those of the skull of this and most other small 

 Birds, does not admit air, as has been frequently stated by Dr. Crisp (various places in ' Proc. 

 Zool. Soc.') : the tables of the bone nearly meet, and the margins are everywhere thickened by 

 solid bone. The furcula of the adult Bird is extremely elegant ; the delicate rami become 

 arcuate below their middle ; the compound upper part is very broad, and is emarginate above, and 

 the inter-clavicle has grown into a large, oblong plate, directed equally upwards and backwards 

 so as to touch the keel of the rostrum. 



In Plate XV, fig. 16, the Shoulder- and Breast-bones of the Blackbird (Turdus meruld) are 

 shown, as seen from below, magnified ten diameters ; these are at nearly the same stage as the 

 parts of the second embryo of Linota (figs. 13 15). The scapula (sc.) is much less pointed; 

 the coracoid (cr.) is more massive ; the prse-coracoid segment (p. cr. s.) is seen wedged in between 

 the clavicle and head of the coracoid ; in a side view it would appear projecting forwards. The 

 clavicles (cl.) have united to form a U-shaped furcula, at the angle of which a small inter-clavicle 

 (i. cl.) is seen. As in Linota, the Sternum is broader than long ; it has one pair of notches, 

 which are, however, almost converted into fenestee by the outspread (pedate) ends of the outer 

 and middle xiphoids. This latter plate (m. x.) has already an arcuate outline behind, and the 

 former (e. x.) is very broad and expanded. The costal processes (c. p.) are angular ; there are 

 five pairs of condyles (c. c.) ; the keel (k.) is low, and outspread behind; and the rostrum (r.) is 

 rather shorter than in Linota. Fig. 17 gives an oblique side view of the Sternum of a fledgling 

 Blackbird (magnified two diameters) ; and in it are seen the three typically Passerine osseous 

 centres. Each " pleurosteon " (pi. o.) reaches fore and aft from the end of the costal process 

 (c. p.) to the verge of the xiphoid notch ; below it has met the azygous " lophosteon " (lo.) which 

 ossifies part of the body of the bone, the rostrum (r.), and the whole of the keel (k.). Already 

 the xiphoids (m. x., e. x.) are wider apart, and the whole of the Sternum is more gblong; in the 

 adult this becomes intensified, and then the largely pedate external xiphoids stand well forwards 

 as well as upwards, these processes becoming almost as far advanced as in the Gallinacea3. In the 



