154 SHOULDER-GIRDLE AND BREAST-BONE. 



I shall speak of the Shoulder-bones of these two great Families together, for they are 

 intimately related, and both have one common origin, namely, in the simple Pluvialine type. 

 When I have described the structure of these oceanic modifications of the Plover, I shall describe 

 the development of the parts in the simple, radical type, and then pass on to the nobler forms 

 of wading and running genera that grow from the same root (see 'Trans. Zool. Soc.' 1863, 

 p. 149). The Albatross and its relatives show the Pluvialine type in its greatest degree of 

 oceanic modification ; whilst the Larinae are directly connected to the Plovers by Glareola. 

 In Diomedea exulans the scapula is long, very narrow, and much curved ; but the coracoid has 

 a perfectly Lacertian expansion ; this is seen also to a less degree in Procellaria capensis, 

 and in Puffinus brevicaudus ; in Pelecano'ides it is much narrower. In all these the meso- 

 coracoid is well developed as a curled spur, and the " foramen " is pierced through solid bone. 

 The rami of the furcula are as curved in Pwffinus as in the Gulls, and it has the same develop- 

 ment of the " prae-coracoid " but this part is less developed in the more typical Petrels, and the 

 rami are straighter. In Puffinus the angle of the furcula is free of the Sternum, and has a well- 

 shaped inter-clavicle ; but in the others this last part is more or less aborted especially in Pele- 

 cano'ides, and the angles of the furcula and sternal keel are articulated together by a synovial joint. 

 The Procellarinse agree in having a small rostrum to the Sternum ; the coracoid grooves are some 

 distance apart ; the keel is strong, broad, and flat below, apiculated at its apex, and reaching 

 nearly the end of the mid-sternum. The costal processes are sharp, and are followed by five or six 

 condyles ; the whole shape of the Sternum is squarish and broad ; longest in Pelecano'ides, but 

 little expanded between the ribs in Procellaria capensis and Pwffinus; considerably widened 

 in Diomedea, and very much so in Pelecano'ides. The xiphoid processes agree with those of the 

 Gulls in Puffinus, that is, they are five in number, separated by large semioval notches ; and the 

 intermediate bar is only half the size of the outer. In Procellaria capensis there is this differ- 

 ence, namely, the notches are small, and consequently the processes are short. In Diomedea 

 exulans the middle xiphoid is short and trifid; the intermediate and outer parts form one large 

 flap, separated by a semicircular notch from the middle part, and have a sub-lateral fenestra on 

 the right, and a minute notch on the left side. In Pelecano'ides, with its longer Sternum and 

 elegantly dilated xiphoid region, there is only a slight emargination at the mid-line, and a gentle 

 sinuosity on each side of this notch ; there is no other notch or fenestra in the adult, but there are 

 two large fenestrae in the young : the broad outer xiphoids are not ossified behind. The middle 

 part of the Sternum is most arrested in Diomedea ; but it is greatly expanded in front in that genus. 



One description will serve for the six types of Larinae mentioned above. The ensiform 

 scapula is considerably curved, and its acromion is blunt ; the coracoid is elegantly phalangoid ; 

 has a large head, and a large flat meso-coracoid, which nearly forms a ring with the head of 

 the bone ; the foramen is pierced in solid bone ; the epicoracoid region is moderately broad, 

 and there is a delicate upturned hook. The furcula has well-marked thickenings derived from the 

 meso-scapula and proximal prae-coracoid segments; its rami form a third of a circle in their 

 curve ; they are strong, oval in section, and have at their angle a semioval interclavicle, which 

 does not reach the sternal keel. The Sternum is a neatly oblong bone, one third longer than 

 broad ; its keel is deep, and the apex is produced forwards, whilst its posterior part reaches the end 

 of the middle xiphoid. The rostrum is large and semioval ; the costal processes rather square 

 and large ; there are six condyles in Bissa, Gavia, and Glareola, and five in Larus argentatus. 



