1907.] TO THE OSTEOLOGY OF BIRDS. 369 



is by oblique facets, so that the posterior half of the inner wall of 

 the foramen is bounded by a spine-like projection fashioned out 

 of the acromion, — the inner side of the spine forming the articular 

 surface for the furcula. 



vi. The Pelvic Girdle. 



The pelvic girdle presents no very striking modifications, 

 neither does it afford any important structural characters such as 

 can be of use for systematic purposes. But there are nevertheless 

 features which deserve mention. 



In the Tyrannidse the pelvis is broad, the ilia being widely 

 separated by the transverse processes of the synsacrum. The 

 pi-e-iliac region is moderately long and varies slightly in its shape 

 in diSerent genera. The superior margin of the fovea iliaca 

 anterior in all, howevei", fades away in the region of the anti- 

 trochanter and is not continued backwards into the free edge of 

 the dorsal plane. The postacetabular ilia are broad, and twisted 

 horizontally to form a broad dorsal plane, and enclose between 

 them a broad plate formed by the synsacrum and its transverse 

 processes. Ossification however has almost completely obliterated 

 the intertransverse saci'al foramina. The ischium is narrow, and 

 has its postero-inf erior angle produced backwards into a long style, 

 which, at its tip, serves as a point of attachment to the pubis. 

 This is long and slender, and is produced backwards for some 

 distance beyond the free end of the ischium. The ischio-pubic 

 fissure is wide and long ; shut ofif anteriorly from the obturator 

 foramen by a bony bar, and closed posteriorly by the junction 

 of the ischium with the pubis. The ilio-ischiadic foramen is 

 relatively large. There is no pectineal pi-ocess. Hhe fovea luin- 

 halis is shallow, and the fovece ischiadica and 2>udendalis pass 

 almost insensibly into one a,nother. 



The pelvis of the smaller forms of the Families now under 

 considei'ation does not differ materially from that just described 

 as typical of the Tyrannidse. In lai'ger birds, such as the Gym- 

 norhinse, the girdle is relatively much longer, while the pre-ilia 

 rise lip to the level of the syn sacral ridge, nearly meeting one 

 another in the middle line. There is a single row of intertrans- 

 verse sacral foramina ; the ischio-pubic fissure is very wide, and 

 closed postei'ioi'ly, but it is not shut off from the obturator foramen 

 by a bony bar. 



That the form of the pelvis may be veiy largely modified by the 

 decline of the power of flight and the consequent increased use of the 

 hind limbs, may be seen in the pelves of such birds as Euryceros 

 prevostii and Newtonia brunneicauda. Both these species would 

 seem to be relatively poor fliers, inasmuch as the carina sterni is but 

 feebly developed : and this is especially true of Neiotonia brunnei- 

 cauda — one of the Muscicapid?e wherein the keel of the sternum 

 is remarkably shallow. Here the width of the pelvis is increased 

 by the lateral extension of its dorsal plane, while greater depth is 



