1899.] OSTEOLOGY OF THE TUBI^ARES. 399 



The coracoid is of great width across the base. This is especially 

 the case in those genera which have a notched, sternum ; in these, 

 the shaft is shorter not only in proportion to the width of the 

 base, but also in proportion to the length of the sternum. The 

 width of the base is relatively least in Pelecaaoides, in which it 

 does not exceed half the length of the shaft, and greatest in 

 Diomedea, in which the breadth of the base and the length of the 

 shaft are nearly equal. The procoracoid is large, and there is a 

 supracoracoid foramen. There is no articular facet on the acro- 

 coracoid for the furculum. 



The sccqnda is subcylindrical and flattened at its free end, 

 and about as long as the furculum measured from the hypo- 

 cleideum across to the free end. 



The furculum is U-shaped, and with, or without, a hypocleideum. 



vii. The Pelyio Girdle. 



The pelvic girdle of the Petrels most nearly resembles that of 

 the Sphenisci. The resemblance in the case of the Diomedeidae, 

 however, is less marked, as the pelvis, like the rest of the skeleton 

 in this Family, is more specialized. 



In the Procellariidae, save in Ossifraga, the innominate bone 

 remains free throughout life, and the pre-ilia do not meet in the 

 mid-dorsal line above the synsacrum. The pre- and post-ilia are 

 of about equal length. The ischium is produced far backwards and 

 beyond the post-ilium, and turns sharply downwards to join the 

 pubis, with which its free end is firmly united by ligament. The 

 ilio-ischiadic foramen is large ; the obturator fissure is very wide 

 and opens forward into the obturator foramen. The innominate 

 of the Penguin differs from that of the Petrel in the smaller size of 

 the ilio-ischiadic foramen, and the shorter and wider ischium. To 

 the increase in the width of the latter the narrowness of the 

 fissure is due. 



In Ossifraga the innominate is fused with the synsacrum, and 

 the pre-ilia rise forwards to the level of the neural crest of the 

 synsacrum. 



In Pelecanoides the pre-ilia are reduced to narrow bars of bone 

 articulating with the extreme outer edge of the transverse 

 synsacral ridge, whilst the pubis and ischium are produced directly 

 backwards with a slight downward curve precisely similar to that 

 of the Alcidaj, with which group they also agree in the great 

 length of the posterior thoracic and sternal ribs, thus affording 

 us another instance of the modification of parts by adaptation to 

 similar functions. 



In the Diomedeidae the innominate is not only fused with the 

 synsacrum, but the pre-ilia meet in the mid-dorsal line above its 

 neural crest. The pelvis as a v^hole, on account of this, comes to 

 resemble that of ISula. Other Cicouiiform resemblances have 

 already been pointed out in describing the skull of this family. 

 They suggest a parallel development of characters derived from a 

 common source. 



