REPORT ON THE ANATOMY OF THE PETRELS. 5T 



In the Oeeanitidse the radius and ulna are generally stouter and stronger bones 

 they are in the Procellariidse ; 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 maims (excluding the carpus) is the longest of the three 

 segments, but this is not the case in the larger forms (Adamastor, Majaqueus, and 

 Otssifraga) of the Procellariinae, whilst in the Diomedeinae the manus is very much 

 shorter, as may be seen by the measurements, than either the humerus or ulna. 



Pelvic arch. — The pelvis (cf. PI. VI. fig. 12, pelvis, &c, of Majaqueus cequi- 

 nocticdis) may be described as generally elongated and narrow. The prce-acetabular is 

 about equal to the post-acetabular axis, though in Cymocliorea, Procellco'ia, Pelecanoides 

 and the Oeeanitidse 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 

 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 vertebras, 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- 

 brae. 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 fossae are 

 narrow, fairly deep and confluent. In front they are limited by the transverse pro- 

 cesses of the 3rd or 4th sacral vertebras, 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. 



