OSTEOLOGY OF ANTARCTIC SEALS. 19 



No. 43 OF COLLECTION (MALE). 



The skull is characteristically short and broad. The greatest length was from 

 premaxilla to the occipital condyles, whilst the greatest breadth was between the two 

 zygomatic arches, just at the articulation between its two component parts the zygo- 

 matic process of the temporal and the malar bones. 



A comparison of this skull was made with those of an adult Weddell and sea-leopard 

 in regard to length and breadth an index being framed. Thus, the length-breadth 

 index of the Ross skull was 72'4 ; of the Weddell skull, 62' 13 ; of the leopard seal, 55 '07. 

 The nasals measured 79 mm. long, and were completely ankylosed. They articulated 

 with the frontal and superior maxillary bones. The part between the two frontals 

 amounted to about three-quarters of the entire length of the bones (57 mm.), and was 

 triangular in form, while the remaining quarter between the two superior maxillary bones 

 was quadrilateral. 



The distance between anterior edge of the outer border of the nasals and the tip of 

 premaxilla was 18 mm., the superior maxilla thus forming to this extent part of the 

 outer boundaries of the anterior nares. " The length of the section of the boundary 

 formed by one of these bones varies in the different specimens from 9 to 1 7 millimetres " 

 (BARRETT HAMILTON, Resultats du Voyage du S.Y. " JBelgica," 1897-1899, p. 5). 

 The anterior iiares sloped downwards and forwards at an angle of 59 with the hard 

 palate. In Weddell seal this angle was 48, in leopard seal 35. 



The anterior nares were bounded from above downwards by the anterior border of 

 the nasal bones, part of nasal borders of superior maxilla, and by the premaxillary bones. 

 Looking into the anterior nares, one was struck with two points the thickness of the 

 meso-ethmoid, and the extremely convoluted arrangement of the turbiuate bones. The 

 anterior edge of the vorner was received between the meso-ethmoid and the premaxillary 

 bones. The premaxillary bones supported the two incisor teeth ; their palatal parts were 

 triangular in form, and, as before mentioned, their nasal parts did not extend so high as to 

 meet the nasal bones. The ante-orbital process of the superior maxilla was well marked, 

 and lay in the same transverse plane as the infra-orbital foramen, below which is a 

 definite depression from which a groove leads to the orbital floor. The widest part of 

 the hard palate was situated well behind the last molar, and was 7 mm. in front of outer 

 end of articulation of palatal processes of the superior maxilla and palate bone. It was 

 almost flat, showing only a trace of a concavity. The posterior border of the hard 

 palate was concave, and possessed a faint post-nasal spine. On the norma verticalis of 

 the skull, at the junction of the frontal bones, i.e. at the seat of the anterior fontanelle 

 in the young, is situated an opening between the bones. Its margins are irregular and 

 spiculated (see fig. 1). As there is no history of an injury, the animal not being 

 clubbed, but shot in the thorax, it appears to me to be a persistent anterior fontauelle. 

 In the female Ross seal this condition is only faintly represented, but in the plate of 

 the Ross seal of the Belgian Expedition a similar well-marked deficiency is to be 



(HOY. SOC. EIHN. TRANS., VOL. XLVII., 189.) 



