1898.] osTEOLOGi or the impennes. 961 



is crossed transverse!}' by a ridge of bone. In Oatarrhactes, Pygo- 

 scelis, Aptenodytes, and Eudyptula this ridge traverses the region 

 of the lambdoidal suture, and may be called the lambdoidal ridge. 

 In the adult it forms a line roughly dividing the cerebellar from the 

 cerebral dome. In Splieniscus the ridge traverses the region of the 

 coronal suture, and may be called the coronal ridge. In young birds 

 both a lambdoidal and a coronal ridge exist together for a short time ; 

 later, by the deepening of the temporal fossa posteriorly, the latter 

 becomes the free edge of the squamoso-parietal wing. 



The supra-orhital region of the cranial roof presents some 

 important modifications. In all, the frontal is more or less deeply 

 grooved for the nasal gland, the groove running the whole length 

 of the frontal from the parietal forwards to the level of the posterior 

 border of the nasal, and it is with the form and development of this 

 that we have now to deal. In Aptenodytes (PI. LIX. fig. 3) the free 

 edge of this groove is reflected up and runs forwards as a narrow 

 tapering supra-orbital ledge for the whole length of the groove. 

 In Eudyptula (PI. LIX. fig. 4) and Splieniscus magellanicus 

 (PI. LIX. fig. 1) this ledge disappears almost immediately after 

 its origin. In Splieniscus demersus the ledge takes the form of a 

 very broad lateral expansion abruptly truncated in front, in the 

 region of the posterior third of the groove. In Catarrliactes 

 (PI. LIX. fig. 5) and Pygoscelis (PI. LIX. fig. 2) this ledge has 

 greatly increased in width, and runs forwards to within a short 

 distance of the lachrymal : moreover, its free edge has become 

 flattened dorsally into a very distinct rim. This reaches its greatest 

 development in Pygoscelis papua (PI. LIX. fig. 2). In all, the 

 supra-orbital groove is more or less completely walled in by a 

 ridge of bone posteriorly. In P. adelice this wall is absent. 



The interorbital region of the frontal varies in width, from 

 a broad median strip of bone in Aptenodytes to a sharp ridge 

 in P. adelice. 



The outline of the supra-orbital ledge is continued forwards by 

 the lachrymal. In Catarrliactes clirysocome (PI. LIX. fig. 5) and 

 Pygoscelis tamiata this latter is largely visible in a dorsal view. 

 Less of it is seen in C. chrysolop/ms, Aptenodytes, Eudyptida, and 

 Pygoscelis papua (PI. LIX. fig. 2). It is largely visible in P. 

 adelice, and has quite disappeared beneath the nasal in Splieniscus. 



The posterior ends of the nasals are not distinguishable in the 

 adult Penguin. The extreme posterior ends of the nasal process 

 of the premaxilla can apparently always be made out lying between 

 the nasals, except in very old specimens of Splieniscus demersus, 

 where they are indistinguishable. In Aptenodytes and Pygoscelis 

 the two prongs of this region of the premaxilla remain distinct 

 one from another and from the nasals throughout life (PI. LIX. 

 figs. 2 & 3). 



The Basioccip>ital Region. — When seen from below, this is bounded 

 in the adult, on all sides, by a raised bony wall. JBehind lies the 

 occipital condyle, laterad of this a pair of mammillary processes, 

 furnished by the exoccipitals, and immediately in front of these 



