REPORT ON THE ANATOMY OF THE PETRELS. 51 
In the Oceanitide the radius and ulna are generally stouter and stronger bones 
they are in the Procellariidee; the former is considerably expanded at its distal 
extremity. 
As may be seen by the table at the end of this section (p. 54) the three chief segments 
of the fore-limb are, as a rule, nearly equal in length, this being especially true as regards 
the arm and forearm. 
Pelecanoides alone has the latter much shorter than the arm, the proportions here 
being three to four. In all the others the humerus and ulna are nearly equal in length. 
In most of the genera the manus (excluding the carpus) is the longest of the three 
segments, but this is not the case in the larger forms (Adamastor, Majaqueus, and 
Ossifraga) of the Procellariinze, whilst in the Diomedeine the manus is very much 
shorter, as may be seen by the measurements, than either the humerus or ulna. 
Pelvic arch.—The pelvis (cf. Pl. VI. fig. 12, pelvis, &c., of Majaqueus equi- 
noctialis) may be described as generally elongated and narrow. The proe-acetabular is 
about equal to the post-acetabular axis, though in Cymochorea, Procellaria, Pelecanoides 
and the Oceanitidze it is considerably longer. In Puffinus, on the other hand, the reverse 
is the case. 
The ilia are long and narrow; anterior to the acetabula they are slightly concave 
plates, with their anterior extremities somewhat rounded off, separated mesially by the 
sacral vertebrae, the neural spines of which coalesce into a strong median ridge The 
antitrochanteric eminences are strong, and stand out conspicuously, the iliac bones 
attaming here their greatest transverse extent, though each bone is narrow and 
separated by a wide space, occupied by the bodies and transverse processes of the more 
posterior sacral vertebrae, from its fellow of the other side. A strongly marked post- 
acetabular ridge runs from here inwards and backwards to the prominent posterior iliac 
angle, which lies between the transverse processes of the second and third caudal verte- 
bre. External to the ridge, the iliac surface is nearly vertical. 
The ischia are narrow and compressed plates of bone, usually strongly curved down- 
wards posteriorly to articulate with the dilated posterior ends of the nearly straight, 
slender, pubic bones, each of which has at the level of the anterior angle of the acetabu- 
lum, a slight prepubic spine. The posterior ilio-sciatic margin is first strongly concave 
backwards, and then convex. 
Seen from below, the pelvis preserves its generally narrow shape, the pubes being 
only slightly inturned at their posterior, cartilaginous extremities. The renal fossz are 
narrow, fairly deep and confluent. In front they are limited by the transverse pro- 
cesses of the 3rd or 4th sacral vertebrae, which, like those of their predecessors, are 
short and slender, the 7th, 8th, 9th and 10th of those bones developing transverse 
processes, which abut against the ilia, and in the larger forms become strong and more 
or less double. 
