THE VOYAGE OF THE 'CHALLENGER.' 423 



Pelecano'ides alone has the latter much shorter than the arm, the pro- 

 portions 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 Procellariinae, whilst in the 

 Diomedeinae the inanus is very much shorter, as may be seen by the 

 measurements, than either the humerus or ulna. 



Pelvic Arch. The pelvis (cf. PI. XXII. fig. 5, pelvis &c. of Majaquem 

 cequinoctialis) may be described as generally elongated and narrow. The 

 prae-acetabular is about equal to the post-ace tabular axis, though in 

 Cymochorea, Procellaria, Pelecano'ides, and the Oceanitidae it is consider- 

 ably 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 attaining 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 back- 

 wards to the prominent posterior iliac angle, which lies between the 

 transverse processes of the second and third caudal vertebrae. External 

 to the ridge, the iliac surface is nearly vertical. 



The ischia are narrow and compressed plates of bone, usually strongly 

 curved downwards 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 acetabulum, a slight prepubic spine. 

 The posterior ilio-sciatic margin is first strongly concave backwards, and 

 then convex. 



Seen from above, the pelvis preserves its generally narrow shape, the 

 pubes being only slightly inturned at their posterior, cartilaginous 

 extremities. The renal fossae are narrow, fairly deep, and confluent. 

 In front they are limited by the transverse processes 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. 



There is not very much divergence from the general form of pelvis Zool. Chall. 

 described here amongst the various forms of Petrels. In the Albatrosses Esp.jol.iT. 

 it becomes very narrow, especially anteriorly, the renal fossae being cor- 

 respondingly narrow and deep. The bones entering into its composition, 

 and supporting it, become extensively pneumatic. Anteriorly the ilia 



