496 DR. R. O. CUNNINGHAM ON THE ANATOMY 
supraoccipital consists of an upper, somewhat quadrangular plate, from which proceed 
downwards two processes which together cireumscribe the upper (and larger) portion 
of the foramen magnum, and have their outer borders deeply excavated by the occipital 
fontanelles. ‘The exoccipitals are rather irregularly shaped bones, which adhere closely 
to the periotics. The basioccipital presents a somewhat triangular figure. Its anterior 
third is covered by the posterior part of the combined basitemporals; and its apex bears 
the central portion of the occipital condyle. In the crania of flying birds the supra- 
occipital is anchylosed to the exoccipitals, but is still separated from the parietals. 
I am not aware that the basisphenotd offers any special peculiarities, consisting, as is 
commonly the case, of a triangular body, formed of a superior and two inferior portions 
(which are anchylosed in the youngest specimens examined), and of a long rostrum, 
which forms the basis of the interorbital septum. The under surface of the triangular 
body is much flatter than in the Muscovy Duck. The alisphenoids are distinct bones in 
the two youngest specimens, but fully anchylosed to the basisphenoid in the adolescent 
flying birds, in which, however, they are only partially united to the frontals and 
squamosals. ‘They constitute the major portion of the postorbital processes. 
The pre- and orbito-sphenoids are not ossified in the youngest crania, while in the 
skulls of the adolescent and adult birds they unite with the ethmoid to form the inter- 
orbital septum. 
The ethmoid in the youngest specimens presents much the same form which obtains 
in nestling individuals of many other birds, consisting of a (lozenge-shaped) horizontal 
and of a yertical plate. In the crania of adolescent birds the vertical plate has blended 
with the elements of the anterior sphenoid, as already stated ; but the horizontal, which 
has now assumed an ellipsoidal form, is not anchylosed to the bones (frontals and nasals) 
which roof it in. 
The interorbital septum in young birds, as may be gathered from what has been just 
stated, is almost entirely membranous. In adolescent individuals it is thin, and pre- 
sents several large apertures, while in adult birds it is very fully ossified, in some 
instances only possessing a single vacuity of any considerable size, situated immediately 
in front of the foramen for the optic nerves’. 
The vomer is of the usual form, as may be seen by the figure, but is of larger size 
than that of the generality of Ducks. 
The parietals, like the other bones, are distinct in the youngest specimens; and a 
small lozenge-shaped fontanelle occurs in the middle line of the upper surface of the 
cranium, between their upper extremities and the posterior internal angles of the 
frontals. They are irregularly triangular in form, their narrow curved base resting on 
the squamosal, and its anterior angle being intercalated between the frontal and that 
bone. In adolescent birds they are anchylosed to the squamosals, only a trace of the 
* The interorbital septum in Biziura lobata is much more feebly ossified than in any of the other Anatide 
examined by me, 
