1898.] OSTEOLOGY OF THE IMtENTSllS. 979 



Except in Pygoscelis papua, the innominate bones remain widely 

 separated by, and free from, the synsacrum throughout Ufe. The 

 pre-ilium in no case quite reaches the fused neural spines of the 

 synsacrum ; in Aptenodytes the pre-Uia are more markedly separate 

 than in any other genus. 



In a nestling Aptenodytes the acetabulum is bounded, anteriorly 

 by the pre-ilium, posteriorly by the ischium and pubis. The 

 ischium bears a share in the formation of the antitrochanter. 

 The pubis is nearly as broad as the ischium and only slightly 

 longer ; the post-ilium falls far short of the hinder end of the 

 ischium, from which it can be easily distinguished by a faint line 

 running forwards to the ilio -ischiadic foramen. It is noteworthy 

 that it is not divided by a fissure from the ischium as in the 

 young of many other birds, or as in the case of the Struthious 

 birds and Tinamous. This is probably a secondary feature due 

 to the extreme backward rotation of the ischium and pubis. The 

 anterior and posterior renal fossae are not sharply defined. 

 The synsacral foramina in the acetabular region are minute. The 

 form of the pelvis is very uniform throughout the group : such 

 points as are of systematic value will be found in the appended 

 " Keys." 



Fig. 1. 



Lateral view of the innominate of a nestling Catarrhaotes chrysocome, 



to show the separate elements. 



ant., anti-trochanter ; ad., acetabulum ; il., ilium ; is., ischium ; pb., pubis. 



vii. The Pectoral Limb. 

 The bones of the wing in the Impennes can only very 

 imperfectly be distinguished either specifically or generically one 

 from another. The wing of Aptenodytes can be distinguished 

 from that of any other genus by its superior size, the humerus 

 being not less than 4--i inches in length. That of Pygoscelis papua 

 comes next, being 3-5 in. Except in the slightly superior size of 

 the pneumatic fossa, the wing of the smaller species of Pygoscelis 

 cannot be distinguished from that of OatarrJiactes or Spheniscus. 

 The last two genera are almost indistinguishable one from another. 

 That of Splieniscus may perhaps be distinguished from that of 

 Catarrhactes by the size of the ulnare. This, in all, is triangular in 

 shape, but in Spheniscus only, apparently, is the width of the 

 base — the postaxial border— but slightly greater than the height ; 



