EEPORT ON THE SPHENISCID^. 25 



great development of the scapular muscles. The relatively large size of the bone is due 

 to increase in breadth rather than in length, the latter remaining much the same as 

 in other birds. 



In Eitdyptes chrysocome ^vom. Tristan d'Acunha (PI. VII. fig. 1), the bone is scimitar- 

 shaped, and increases in breadth from the narrowest j)oint or neck, which is situated 

 immediately behind its articular extremity, nearly to the posterior extremity of the bone. 

 The bone is much flattened, and presents two surfaces — an external and an internal, both 

 of which are rough and uneven, for the attachment of muscles. Immediately in front of 

 its narrowest point, the scapula expands in breadth, and develops its articular facets. 

 These are arranged in the manner common to birds. The inner of the two articular sur- 

 faces articulates with the extremity of the clavicle, while the outer, which is separated from 

 the inner by a shallow notch, is divided by means of a vertical ridge into two parts. 

 Of these the internal articulates with the shaft of the coracoid bone, while the external 

 contributes to the formation of the glenoid fossa for the reception of the head of the 

 humerus. The posterior angle of the scapula extends in Eudyptes chrysocome as far 

 back as the sixth vertebral rib, which it slightly overlaps. 



The form of the scapula varies considerably in different Penguins. 



In every member of the genus Eudyptes (PL VII. fig. 1) the scapula agrees in form 

 with that of Eudyptes chrysocome. In this genus the bone increases in breadth some- 

 what abruptly. The posterior border of the bone is obliquely truncated from above 

 downwards and forwards, and the angle between the superior and posterior borders of 

 the blade of the scapula projects farther backwards than any other portion of the bone. 



In Spheniscus (PI. VII. fig. 2) a posterior border of the scapula can hardly be 

 said to exist, the superior and inferior borders of the bone meeting together posteriorly 

 to form a rounded angle which forms the posterior extremity of the bone. 



In Aptenodytes (PL VII. fig. 4) the scapula more closely resembles that of 

 Eudyjytes than of Spheniscus. In it the bone expands more gradually from the neck to 

 the blade than in Eudyptes, but its posterior border is even more clearly defined than in 

 that genus. In Aptenodytes, however, the posterior border of the scapula forms nearly a 

 right angle with both the superior and inferior borders of the bone, and is less obliquely 

 truncated than in Eudyptes. In Spheniscus the reverse is the case, the posterior 

 border of the scapula in that genus being indistinguishable because of the coalescence 

 of the superior and inferior borders of the bone. 



In Pygosceles (PL VII. fig. 3) the scapula difi"ers from that of the three other 

 genera, inasmuch as it is relatively shorter and broader, the blade of the bone as distin- 

 guished from the neck expanding more abruptly from the neck than in the other 

 genera. The angle, moreover, which forms the posterior portion of the bone is the angle 

 between the inferior and posterior borders of the scapula, whereas in Eudyptes and 

 Aptenodytes it is the angle between the superior and posterior borders of the scapula. 

 Lastly, in Pygosceles the superior border of the scapula resembles that of Spjheniscus 



(ZOOL. CHALL. EXP. — PAKT XVIU. — 1883.) S 4 



