SKULL OF PENGUINS. 17 



than a passing notice. In the skull of the nestling just referred to, this bone is oblong 

 in shape, broadest along its parietal border, and gently hollowed along three sides 

 (PI. fig. 6). Its posterior border articulates with the lateral occipital, which is yet 

 chiefly cartilaginous, while the anterior border is embedded "in the cartilaginous 

 alisphenoid. In the skull of a nearly full-grown bird in the Museum collection, 

 obtained during Eoss' Antarctic Expedition of 1839-43, the separate elements of the skull 

 are still free, though ossification is complete a fact of no little interest and some 

 importance and here (PI. fig. 8) the squamosal has retained the same general shape 

 as in the younger specimen. But it has assumed, externally, a shallow trough shape, 

 the hollow forming the major portion of the " temporal fossa," and it has at the 

 same time thrown out a thickened phlange of bone immediately above the squamosal 

 articulation for the quadrate ; this phlange forms the superior limb of a >-shaped bony 

 protuberance which ultimately passes into the " paroccipital " process. The parietal 

 border is produced forwards to form a sharp angle, whose apex is separated from the 

 frontal only by a narrow wedge formed by the parietal. 



The significance of this can only be appreciated by a comparison of the squamoso- 

 parietal relations in other species (PI. figs. 1-8). Unfortunately, at present, I cannot 

 make this comparison as comprehensive as could be wished ; but nevertheless one or 

 two interesting facts have come to light out of the material to hand. 



In the skull of a full-grown Pygoscelis papua, in which no fusion of the roofing 

 bones of the skull has taken place, the squamosal is roughly T-shaped, the superior 

 edge of the backwardly directed limb articulating with a long, oblique, and downwardly 

 directed edge provided by the parietal (PI. fig. 5). But between the anterior angle of 

 the superior border of the squamosal and the frontal there is interposed a broad parietal 

 border. Catarrhactes agrees with Pygoscelis in this respect, but in the former genus 

 the squamosal is oblong with a slightly hollowed posterior border (PI. fig. l). 



Pygoscelis adelice, it is to be noted, resembles Catarrhactes rather than its ally 

 P. papua, in so far as this region of the skull is concerned, since, as in Catarrhactes, 

 the alisphenoidal border of the parietal is sharply truncated, and this is a fact which we 

 would hardly have expected. 



That there is some underlying principle involved in the variations met with in this 

 region of the skull is highly probable. At present we can only hazard a guess as to 

 what this principle may be ; but it is not unlikely that we shall be near the truth in 

 assuming that in the skull of Pygoscelis we have a more primitive type than in 

 Aptenodytes or, indeed, of any other penguins except perhaps Eudyptula, which has not 

 yet beea examined. The evidence for this is based upon the characters now under 

 discussion, which, adopting Dr. Chalmers Mitchell's method of analysis, we may regard 

 as a metacentre, while the apocentricities arising therefrom are multiradial. 



I have fixed, rightly or wrongly, on Pygoscelis papua as the point of departure 

 of this metacentre, for the following reasons. In this skull the squamosal 

 articulates with the parietal by means of a long oblique suture, sloping from behind. 



VOL. II. P 



