154 GENERAL OBNITHOLOGY. 



ischium, and pubis, which have iudepeudent ossific centres, but become fii-raly consohdated 

 together to form the haunch-bone or os innominatum. Each of these bones unites with the 

 other two, somewhere near the middle of the whole affair, at a ring-like structure called the 

 acetabulum (Lat., a vinegar-cruet, fig. 56, a; fig. 60, arrow ac), which all three consequently 

 contribute to the formation of, and which is the socket for the head of the thigh-bone (femur, 

 p. 135). When free ribs issue from under cover of the pelvis, they are commonly anchylosed 

 with the ilia ; and all the abortive pleurapophyses of the lumbar and uro-sacral vertebrae have 

 likewise iliac anchylosis, as explained in treating of the sacrum (p. 146). As a whole, the pelvis 

 varies like the sternum in relative length, breadth, and degree of convexity ; and especially in 

 the configuration of its posterior border ; but few zoological characters are derived from this 

 structure. 



Viewed from below, the pelvis is seen to be much hollowed or excavated for the lodgment 

 of the kidneys, and cross-cut into compartments by the sacral rafters ; the series of sacral 

 bodies forming a ridge-pole along the middle line. Above, the series of sacral spinous pro- 

 cesses represent the ridge-pole ; anteriorly, the somewhat spoon-shaped iliac bones are 

 applied, concavity outward, to the dorso-lumbars ; posteriorly, in the middle line, is a more or 

 less flattened horizontal expansion, and laterally are the more expanded sides of the ischiac roof, 

 finished along the eaves and behind by the slender pubic bone, whicli commonly projects 

 backward, and inclines toward its fellow of the opposite side. The most prominent formation 

 of the side wall of the pelvis is the thick-hpped smooth articular ring, the acetabulum, con- 

 verted in the natural state into a cup by a membrane. 

 The postero-superior segment of the rim is promi- 

 nent, to form the antitrochanter (Gr. avri, anti, 

 against; Tpoxavrrjp, trochanter of the ^emur) against 

 which the shoulder of the femur abuts when the 

 Fig 61. —Pelvis of yoiinp grouse, showing j^g.^^| jg -^^ ^^^^ ^.^ 

 three distinct bones. II. Is, P. ilium, ischium, ' ^' /- • i • j i 



pubis. In front of former a dorsal vertebra pro- It is normal to recent C armate birds to have 



trudes. (Dr. E. W. Shufeldt, U. S. A.) ^j^g ischium fused with the ilium, however distinct the 



pubis may remain ; but to Cretaceous birds (even the carinate Ichthyornis), and l^e existing 

 RatitcE, to have both ischium and pubis distinct in most of their extent. 



The Ilium (Lat. ilium, haunch-bone ; pi. ilia ; adj. iliac ; figs. 56, I; 60, 61, II) is the 

 median, most anterior and longest of the haunch-bones, and the only one which extends in ad- 

 vance of the acetabulum. Such anterior prolongation of this bone is the specialty of the avian 

 pelvis : it commonly overlies one or more ribs, and is often overreached by the end of the scapula. 

 It is longest and narrowest and flattest in some of the lower swimmers ; the reverse among the 

 highest birds. Its relations and connections have been sufficiently indicated. The bone is 

 almost always separated from its fellow by the sacrum, though the approximation may be 

 very close over the back of tlie j)clvis, along the middle line. 



The Ischium (Gr. la-xiov, ischion, the haunch-bone; pi. ischia ; adj. ischiadic, ischiatic, 

 better ischiac; figs. 56, 60, 61, Is) lies entirely post-acetabular, or behind the socket which it 

 contributes to form, and composes most of the side-wall of the pelvis thence to the end. It is 

 generally a thin, plate-like bone. Among Cretaceous birds and existing Eatitae it only unites 

 with the ilium at and just behind the acetabulum, whence a deep ilio-ischiac fissure between 

 the two exists, as in the young grouse, fig. 61 ; but in ordinary adult birds this fissure is con- 

 verted into a fenestra or window of large size, just behind the acetabulum, by union of the two 

 bones behind it. This vacuity, whether a notch or a hole, corresponds to the ' ' sacro-sciatic 

 notch" of human anatomy (fig. 56, in). The ischia of opposite sides are distinct, except in 

 Bhea. 



