REPORT ON THE ANATOMY OF THE PETRELS. 43 



The skull above the orbits is always deeply excavated for the fossae in which lie the 

 nasal ("supra-orbital") glands. In the Albatrosses there is a strong raised external 

 border to the fossa posteriorly, prolonged from the post-orbital processes, whilst 

 externally this floor, here perforated by numerous apertures, is deeply excavated. 



The post-orbital processes are large and strong. The temporal fossae are well- 

 developed, nearly meeting across the middle line in most, though in the Albatrosses 

 separated by a considerable interval. The occipital plane is inclined downwards and 

 forwards, but in the Albatrosses is nearly vertical. In these birds the digastric fossa; are 

 continuous, meeting each other in the middle line, whilst in the other Tubinares they 

 are separated to a greater or less extent by the wide, smooth, convex cerebellar 

 eminence. 



As might be expected, all these fossae and their bounding ridges are much better 

 developed in the large Albatrosses and Petrels (Ossifraga, Majaqueus, &c.) than in the 

 small Procellariese and Oceanitida?, in which the skull is comparatively smooth, of much 

 thinner texture, and with the cerebellar eminence occupying a much greater extent 

 comparatively. The interorbital septum is well ossified in the larger species, most so in 

 Diomedea exulans, whilst in the smaller ones it is very extensively fenestrated. 



The lachrymal bone is always well developed, but varies in form in the different 

 groups. In the Oceanitidse and the small Petrels of the ProceZfom'a-group it is T- 

 shaped in form, the long arm of the T being horizontal, extending forwards from 

 the body of the bone (which is nearly vertical) to articulate with the external 

 descending process of the nasal bone, just behind the level of the end of the nostril. 

 Between it and the rest of the skull lies a considerable oval fenestra, occupied by membrane 

 in the recent state. The ascending process articulates with the frontal, forming a well- 

 marked, backwardly-directed, antorbital process, whilst the descending process descends 

 downwards towards the jugal arch, to which it maybe united by ligament articulating 

 internally with the considerable antorbital plate of the ethmoid (" ectethmoid," Parker). 



In Pelecanoides, Puffinus, Adamastbr, and Majaqueus it has the same relations, but is 

 more triangular in form, and closely abuts on the cranium superiorly, the fenestra being 

 reduced thus to a chink. In the Albatrosses it also remains separate from the skull, 

 and the anterior limb is but little developed as compared with the vertical part, which is 

 swollen, excavated by air-cells, and forms above a strong antorbital process. It loses its 

 connection with the ethmoid. In the remaining genera the lachrymal does not exist as 

 a free bone, being firmly anchylosed to the frontal above and the ethmoid anteriorly 

 (PI. VI. figs. 1, 3). It is hollow, with one large, and several small, external apertures. 



In connection with the descending limb of the lachrymal bone.'thcre is often developed 

 a peculiar ossicle, named by Brandt (cf. sui^m, p. 5), who was the first to describe 

 its existence in Diomedea brachyura and Puffinus major, the "ossiculum lacrymo- 

 palatinum," from its connection with those two bones. 



