1898.] OSTEOLOGY OF THE IMPENTVTES. 977 



V. The Pectoeai, Girdle and Steentjm. 



The pectoral girdle of the adult Penguin is of the same general 

 form throughout the group. 



The coracoid is a stout bone, typically about half as long as the 

 sternum. The precoracoid is large iu all. In an example of 

 Pygoscelis papua it extends almost the whole length of the coracoid. 

 The supracoracoid foramen is complete in all but Aptenodiites and 

 Pygoscelis. The acrocoracoid is fairly well developed ; in Pygoscelis 

 and Spheniscus magellanicus it forms a conspicuous, downward and 

 inwardly projecting spur. 



The form of the scapula is unique, being of great length and 

 shaped like a scimitar ; the convex border is dorsal, the concave 

 ventral. In Aptenodytes and Pygoscelis it is sharply truncated 

 posteriorly ; in Spheniscus and Eudyptula the inferior angle of this 

 posterior border is rounded off, so that the free end of the bone 

 assumes a somewhat pointed form. That of Catarrhactes can be 

 more or less distinguished from that of Spheniscus by the greater 

 curvature of its superior border, and the acute angle formed at 

 the hinder end of the inferior border, giving the scapula a truncated 

 appearance posteriorly, similar to that of Aptenodytes. In 

 C ch7'ysolophus, however, this is less marked, and makes it some- 

 what difficult to distinguish from the scapula of Spheniscus. 

 There is a well-marked acromial process for the articulation of 

 the free end of the clavicle. 



The /wrcwZa is U-shaped and much curved, its convexity looking 

 forwards and downwards. There is no hypocleideum. Its free end 

 forms a slight roughened expansion for articulation with the 

 acromial process of the scapula. Ventrad of this is a more or less 

 oval irregular surface for articulation with the acrocoracoid. Prom 

 the level of this articulation downwards, the limbs of the furcula 

 are laterally compressed, but they gradually take on a rounded form 

 as they approach the symphysis. 



The sternum is about half as broad as long, with a pair of notches 

 posteriorly. The keel in all cases projects beyond the corpus 

 sterni. In Aptenodytes this is a very marked feature indeed, the 

 anterior border sloping obliquely forwards and downwards for 

 about one-sixth of the total length of the sternum. In all but 

 Aptenodytes there is a well-marked spina externa. This is more 

 or less marked by the forward continuation of the keel. In some 

 it is well marked. In Aptenodytes the anterior border of the keel 

 passes directly into the corpus sterni. The form of the spina 

 externa and of the anterior border of the keel is very variable, 

 even among species of the same genus, so that no value can be 

 placed on it as a systematic factor. There is no spina interna. 



The anterior lateral processes project forwards and outwards, the 

 base of each on either side runs from the inner end of the coracoid 

 groove outwards to the external border of the corpus sterni. 

 Along this border, at the point where the two regions may be said 

 to meet, is placed the articular surface of the sternal segment of 



