1898.] OSTEOLOGY OF THE IMPElS'JfES. 959 



So much is known already about the osteology of the Penguins, 

 thanks to the admirable memoirs of Watson (18) and Menzbier 

 (13), that it will not be necessary to describe the bones in any 

 great detail ; rather, it will be the aim of the present paper to 

 serve as a supplement to those just mentioned. 



ii. The Skull of the Adult, 



The skull of the Impennes presents many points in common 

 both with the Pygopodes and the Tubinares, but it can nevertheless 

 be readily distinguished from that of both of these groups. 



The Occipital Reijion. — The occipital condyle is sessile, and scarcely 

 projects beyond the rim of the foramen magnum. In Aptenodytes 

 there is a slight tendency towards a pedunculate condition. The 

 general form of the condyle is reniform : in young specimens 

 traces of the notochord are found in the shape of a small median 

 dimple. 



The foramen magnum is almost circular, but varies slightly 

 in outline. The plane of the foraujen slopes obliquely backwards. 

 Its superior boundary forms the free edge of a well-rounded 

 concavo-convex supra-occipital — the convexity outwards — which 

 forms the characteristic " cerebellar dome." On either side of 

 this dome lie two bony " wings '' or plates which present two 

 distinct types of arrangement. These plates are formed, in part 

 by the squamosal, and in part by the parietal bones (see page 9(38). 



In C'atarrJiactes, the first of the two types, these plates arise from 

 the squamosal prominence 'and run upwards to terminate on the 

 lateral region of the cerebral dome, and are thus separated one 

 from another by nearly the whole width of t'le skull. 



Splieniscus forms the second type. Arising in the same region 

 as the above, these plates have become thrust back, as it were, from 

 the cerebral on to the cerebellar dome, thus placing a wide, 

 deep, space between them and the cerebral dome. This space 

 represents the posterior portion of the temporal fossa, which 

 lodges the temporal muscle. The plate is continued upwards to 

 the vertex of the skull, where, as in S. magellanicus, it joins a 

 median sagittal crest bridging the space from the cerebral back- 

 Avards to the cerebellar dome. 



All the genera but Spheniscus belong to the first type. In 

 C. chrijsocome the cerebellar dome is rather more sharply defined 

 than in any other members of the genus. In C. chrysocome and 

 C. cTirysolopilius, seen in profile, its dorsal moiety appears slightly 

 depressed ; it passes, on either side, almost insensibly into the 

 cerebral dome. In G. scMegell and Megadyptes antipodum the 

 cerebellar arises almost abruptly from the cerebral dome, and its 

 greatest curve is in the centre of the median line, projecting 

 appreciably beyond the level of the foramen magnum. The 

 squamoso-parietal wings of C chrysocome and C. chrysolophus are 

 hardly to be distinguished ; their greatest lateral expansion does not 

 exceed -2 in. and the intervening fossa is narrow ; in C. schlegeK, 



