1898.] OSTEOLO&Y OF THE IMPBNNES. 965 



behind the vomer, the palatines expand into moderately broad 

 plates ; the posterior palatine border is more or less emargiaate, 

 but its exact outline varies. 



The pterygoids are expanded distally into broad plates or 

 laminse, the anterior border of which follows more or less the 

 outline ot the posterior mai-giu of the articular end of the 

 palatine. C. chrijsolophus and Eudijptala appear to be exceptions 

 to this rule. Concerning the early history of the pterygoid, 

 see p. 973. 



The quadrate has distinct otic and squamosal articular heads. 

 The orbital process in Catarrhactes, Eudijptida^ and Splieniscus 

 projects from the main body as a somewhat upwardly-curved rod 

 with a sharp superior border ; that of Pi/(joscell,s closely resembles 

 these but is longer. In Aptenodi/tes it takes on a triangular form, 

 with a thickened inferior border. At the base of the inferior 

 border of tlie orbital process lies a small well-dehned pterapophyseal 

 facet for articulation with the pterygoid. There are two condyles 

 for articulation with the mandible, and these are confluent. The 

 inner has two articular surfaces — an internal lateral facing the 

 median plane, and a ventral which is continued backwards on to 

 the semicircular outer face, immediately above and in front of 

 which lies the deep cup for the articulation of the quadrato- 

 jugal bar. 



The Mandible. — The two rami of the mandible are united by a 

 very slender symphysis. There is a short angular and internal 

 angular process. A dentary, angular, supra-angular, and coronoid 

 can always be distinguished. In young birds there is a distinct 

 splenial. 



In Catarrhactes the posterior border of the dentary is divided into 

 two limbs — a small superior, and a large inferior having a strongly 

 pronounced sinuous border which articulates with the supra- 

 angular, the depth of the jaw in the region of this articulation 

 being very considerable. The deeply incised posterior border of 

 the dentary and the oblique slightly notched border of the supra- 

 angular enclose a lozenge-shaped vacuity which is more or less 

 imperfectly closed from within by the splenial. A second, oval 

 vacuity pierces the supra-angular near its posterior end. Viewed 

 from the inner side, this is seen to lead into an oblong fossa 

 formed by cutting away the superior border of the coronoid ; this 

 fossa leads anteriorly into the dental foramen. The mandible of 

 C. chrysocome can be distinguished from that of C. chrysolophus 

 by the greater convexity of its dorsal border, both dentary and 

 supra-angular having the dorsal border much arched. 



In Pygoscelis the depth of the jaw in the region of the dentary 

 suture is very much less than in Catarrhactes. The superior limb 

 of the dentary suture is relatively longer, and the posterior runs 

 directly backwards with a gentle downward curve. It entirely 

 lacks the strong sinuous border of Catarrhactes. The posterior 

 vacuity is largest in P. antarctica. 



In Aptenodytes the jaw is long and slender. The dentary of 



