No. 5.] SHUFELDT ON THE OSTEOLOGY OF EREMOPIIILA. 137 



metres, to the rounded anterior external angle of the ilium. Between 

 this point and the acetabulum the iliac border is markedly concave in- 

 wards, as is the surface of the bone above it, the preacetabular being 

 included between this border and a well-defined gluteal ridge. The 

 superior postacet abular iliac surface is nearly square in outline, convex, 

 and equal to a little more than one-third of the bone. It is thin and 

 translucent, its outer and posterior borders receiving the greater share 

 of osseous reenforcement, i^articularly in the vicinity of the antitro- 

 chanter. 



Posteriorly, this bone, slightly aided by the ischium, is carried out 

 from an ilio-lschiadic, overhanging crest, as bony processes, with their 

 points turned slightly inwards. 



These processes are strongly marked in another of our Oscines, Har- 

 'porliynclius riifus, a bird that has a notoriously angular and unique pelvis. 



The antitrochanter is subelliptical in outline, and faces downwards, 

 forwards and outwards. The articular surface is produced downwards 

 as far as the cotyloid cavity, upwards slightly above the general sur- 

 face of the ilium, and is bounded posteriorly by the ischiadic notch. 



The foramen at the base of the truly hemispherical cotyloid cavity 

 has so far absorbed the bone that really scarcely anything remains of it 

 beyond a cylindraceous acetabular vacuity, the internal and external 

 apertures being circles of equal diameter, and the femur consequently 

 relying almost exclusively upon its fleshy and ligamentous attachments 

 to retain its head in the ring. 



Sutural traces of the margins of the pelvic bones as the components 

 of this osseous ring have entirely disappeared, having been obliterated 

 during the pelvic consolidation. 



The ischium, for its major joart, is like the ilium — very thin, more par- 

 ticularly so at its free posterior borders ; joining with the ilium behind, 

 it shuts off a large and elliptical ischiadic foramen, the superior arc of 

 which is situated just beneath the ilio-ischiadic crest described above. 

 The major axis of this ellipse is directed downwards and backwards. 



The posterior extremity of the ischium has an odd-appearing, foot-like 

 termination, that is bent down to meet the pudis. 



This latter bone is an extremely slender style, that, immediately after 

 assisting in the formation of the cotyloid ring, closes in a small, in fact 

 the smallest of the group, subcircular obturator foramen behind ; then, 

 running parallel with the ischium, by touching its further end encloses 

 another long spindle-shaped vacuity ; it is Anally produced beyond that 

 bone by a pointed extremity, that curves backwards and inwards. 



It only remains now to say of the pelvis, as far as its internal aspect 

 is concerned — after what we have said in regard to its extreme lightness, 

 its translucency, its sacrum, and its borders — that, in general, superior 

 convexities cause or create internal concavities, and vice versa. It is ca- 

 pacious and firmly united ; any attempt to remove the ossa innominata, 

 in the adult bird, from the sacral border, invariably results in failure and 

 usually longitudinal iliac fracture. 



