4 THE VOYAGE OF H.M.S. CHALLENGER. 



Sphemscus and of Endyptes, and some of the bones oi Aptenodytes. This paper is an ex- 

 tremely valuable contribution, and has to some extent anticipated the conclusions at which 

 I have arrived with regard to the subdivision of the Penguins into genera and s^^ecies. 



More recently MM. Gervais and Alix ^ have published a memoir on the osteology and 

 myology of the Spheniscidse, founded on an anatomical examination of a specimen of 

 Eudyptes chrysolophus. 



The skeleton, either in whole or in part, of one or other species of Penguin will be 

 found figured in the works of Blumenbach,' Brandt,'' Wagner,* Eyton,® and Barkow.^ 



In the works of none of the authors above named, however, can I find any approach 

 to a complete comparative description of the osteology of the various species of Penguin, 

 and this deficiency T now endeavour to make good, so far as the material at my disposal 

 will permit. 



THE AXIAL SKELETON. 

 The Skull. 



The skulls of all the Penguins which I have had an opportunity of examining being 

 accurately figured (Plates I. to V.), it is unnecessary that I should give a detailed de- 

 scription of each. The following observations, therefore, refer only to the leading and 

 distinctive features of the cranial osteology of each member of the group. 



The cranium of every species is completely ossified in the adult, and presents no 

 trace of its original sutures. The form of its exterior closely corrcsj^onds with the outline 

 of the contained encephalon, and indicates externally the subdivision of the latter into the 

 cerebral hemispheres and cerebellum. This correspondence is to a certain extent 

 masked by the develoj)ment of a large transverse ridge, situated on the side of the 

 cranium, to which the squamous, parietal, and occipital bones each contribute a part, as 

 also by the large size of the supra-orbital ledges which accommodate the nasal glands. 

 Apart from these osseous ridges, the correspondence in form between the exterior of the 

 skull and the contained viscus is more striking in the Penguins than in the majority 

 of birds. 



The cerebellar prominence of the skull forms a well-marked osseous dome situated 

 immediately above the occipital foramen. In Eudyptes the most projecting portion of 

 this dome is rounded, while in Sphenisciis it is somewhat sharper and more acute. In 

 Spheniscus minor, however, as in Ap)tenodytes and in Pygosceles, the cerebellar dome 

 jjresents a form intermediate between that which characterises the other species of 



^ Journal de Zoologie, torn, vi., 1877. 



= Hanilbuch der verglcichenden Anatomie, Tab. 3. 



^ Beitrage znr Kenntniss der Katurgeschiclite der Vcigel. 



■* Icoues Zootomies. 



' Osteologia Avium. 



" Syndesmologie der Vogel, 1856. 



