REPORT ON THE ANATOMY OF THE PETRELS. 43 
The skull above the orbits is always deeply excavated for the fossa 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 fossz 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 fosse 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 fossee and their bounding ridges are much better 
developed in the large Albatrosses and Petrels (Ossifraga, Majaqueus, &c.) than in the 
small Procellarieze and Oceanitide, 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 Oceanitide and the small Petrels of the Procellaria-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 les 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 may be united by ligament articulating 
internally with the considerable antorbital plate of the ethmoid (“ ectethmoid,” Parker). 
In Pelecanoides, Puffinus, Adamastor, 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 toa 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 
(Pl. VI. figs. 1, 3). It is hollow, with one large, and several small, external apertures. 
In connection with the descending limb of the lachrymal bonesthere is often developed 
a peculiar ossicle, named by Brandt (cf supra, 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. 
