STRUCTURAL ADAPTATIONS 391 



its finny prey out of the water ; but the Sea Eagles fish in a 

 similar fashion, and the pelvis in these birds, as in the normal 

 Accipitres, is long and narrow by comparison. Again, the Dodo 

 and its ally the Solitaire {Pe.-ophaps) being flightless, were en- 

 tirely committed to terrestrial locomotion, yet the pelvis in 

 these birds is relatively much narrower than in many Pigeons 

 possessing unusually strong powers of flight. Many of the 

 smaller Cuckoos, and many of the Coraciiformes, e.g., the King- 

 fishers, have very broad pelves, yet the Kingfishers certainly 

 cannot be regarded by any stretch of imagination as pedestrians, 

 since the legs in these birds are extremely short, and further- 

 more, the feet, from their peculiar shape, are entirely unfitted 

 for walking. 



Turning now to the members of the Ostrich tribe which 

 are all, save the Tinamous, flightless, we find the giant forms 

 divisible into two groups — those in which the pelvis is extremely 

 broad, and those in which it is extremely narrow, so narrow as 

 to have no parallel among Neognathine birds save the Grebes 

 and Divers ! In the Moas {Dinornis) and in Aipyortiis the 

 pelvis resembles that of the Tinamous in being broad : in the 

 Ostrich {Struihio), Rheas, Emus and Cassowaries, as well as in 

 the pygmy Apteryx the pelvis is extremely narrow. A re- 

 ference to the accompanying figures will bring out this fact 

 better than a mere description. 



The width of the pelvis, we may remark, is determined by 

 two factors: (i) the length of the transverse processes of the 

 vertebrae forming the synsacrum, and (2) by the development 

 of the post-acetabular ilium to form a broad dorsal plate, the 

 " dorsal plane ". 



Where the transverse processes are long, those of the sacral 

 vertebrae are always the longest, those in front and behind 

 gradually increasing and decreasing as they approach and leave 

 this point. But there is not the same uniformity in the matter 

 of the width of the dorsal plane. This may be widest across 

 the anti-trochanters, or at any point caudad of this. Anteriorly 

 these transverse processes may be so long as to prevent the 

 ilia or front ends of the innominate bones coming together, 

 though generally these plates meet one another in the middle 

 line. It would appear that widely separated innominate bones, 

 such as are seen in the figure of the young Boatswain-bird 



