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



dytes it is visible in the upper part of its course. The posterior border of the paLate bone 

 in the genera Eudyptes and Pygosceles is ahnost straight, and articulates with the entire 

 breadth of the anterior extremity of the pterygoid bone. In Spheniscus and Aptenodytcs 

 again, the posterior external angle of the palate bone presents an emarginate notch, and 

 consequently in these genera the posterior border of the palate bone is oblique, and 

 articulates only with the anterior internal angle of the pterygoid bone. 



The inferior free margin of the vomer is grooved anteriorly in every species of 

 Penguin except Pygosceles and Aptenodytes. 



The maxillo-palatine processes present the configuration usually met with in the 

 schizognathous cranium, being slender plates of bone which curve backwards and out- 

 wards without articulating either with one another or with the vomer. 



The maxillary bones approach more closely to the outer border of the palate bone in 

 Eudyptes than in Spheniscus, and hence when the skull is viewed from below, the base 

 opposite the junctions of its cranial and facial portions appears narrower in the former 

 than in the latter genus. In this respect the crania of Aj^tenodytes and of Pygosceles 

 agree with that of Eudyptes rather than with that of Spheniscus. 



The post-orbital process is well-developed in every species, but differs somewhat in 

 form in different genera. In Eudyptes it projects vertically downwards behind the 

 orbit, and is relatively smaller than in Spheniscus, in which, moreover, it is directed 

 obliquely downwards and backwards. In Aptenodytes and in Pygosceles the post-orbital 

 process resembles that of Eudyptes and differs correspondingly from that of Spheniscus. 



The orbital process of the quadrate bone is short and stunted in every species of 

 Eudyptes. In Spheniscus (with the exception of Spheniscus minor) and in Pygosceles it 

 is elongated and pointed. In Aptenodytes and Spheniscus minor the orbital process 

 presents a form intermediate between that of Eudyptes and that of the other species of 

 Spheniscus. In every species of Penguin the upper extremity of the quadrate bone is 

 single, rounded, and not bifurcated. A careful examination shows, however, that the 

 articular surface is divided into two distinct facets — an outer and an. inner — indicating as 

 it were a tendency to that more complete bifurcation of the upper extremity of the bone 

 which obtains in many birds. 



The inter-orbital septum is incomplete in every species of Penguin in consequence of 

 the presence of a large hiatus which is usually almost circular in form. 



The lachrymal bone is T-shaped. It articulates above with the frontal and with the 

 nasal bone, below with the jugal. 



The lachrymo-nasal fossa is triangular in form and of large size. It is bounded above 

 by the external process of the nasal, behind by the lachrymal, and below by the maxillary 

 bone. In Spheniscus it is relatively larger than in Eudyptes. 



The form of the zygomatic arch forms a distinctive generic feature in the skull of 

 Eudyptes as compared with that of Spheniscus. In the former the zygomatic arch is 



