148 GENEBAL ORNITHOLOGY. 



ischium, and pubis, which have iudependent i.i^sific centres, but become finnly consolidated 

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

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

 acetabulum (Lat., a vinegar-cruet, iig. 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. 119). When free ribs issue from under cover of tlie pelvis, they are commonly anchylosed 

 with tlie Uia ; and all the abortive pleurapophyses of the lumbar and uro-sacral vertebras hav(^ 

 likewise iliac anchylosis, as explaiuiid in treating of the sacrum (p. 140). As a whole, the pelvis 

 \'aries like the sternum in relative length, breadth, and degree (jf convexity ; and especially in 

 the configuration of its posterior bca-der ; but few zoological characters are derived from this 

 structure. 



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

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

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

 cesses represent the ridge-pole ; anteriurly, the somewhat spunn-shaped iliac bones are 

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

 less flattened horizontal expansion, ami laterally are the mfire exjiamled sides of the ischiac roof, 

 finished along the eaves and behind by the slender pubic bone, which cominfinly projects 

 backward, and inclines toward its felh.iw iif the (jpposito side. The most pnjminent formation 

 of the side wall uf the ]ielvis is the tliick-lipped smooth articular ring, the acetabulum, cou- 



verteil in tlie natural state into a cup by a membrane. 

 The jjiistero-superior segment of the rim is promi- 

 nent, to fdi'iii th(^ aniifrochaiiter (Gr. dvri, anii, 

 against ; rpuxavTrjp, trochanter of the femur) against 



which the siioulder of the femur abuts wlien the 

 Fio (11. ivlvis of ,„,„,,„ grouse, showing j^g^j j^ ;,., „,,., ^, 

 tliiee aishm.'t lionea. //. /.s-, /'. ilium, iscliuira. - 



pubis. In front of former a ilors.nl vertebni pro- It is normal to recent Carinate birds to have 



tru.les. (Dr. B. w. siiufeLlt, u. S. A.) jj^g ischium fused with the ilium, however distinct the 



pubis may remain ; but to Cretacemis birds (even the carinate Icltfhyornis), and the existing 

 Eatifrc, til have both ischium and pubis distinct in most of their extent. 



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

 median, most anterior and longest of the hauneli-bnnes, and tlie only one which extends in ad- 

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

 pelvis: it commonly overlies fine nr more rilis, 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 cfinncctions liave been sufficiently indicated. The bone is 

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

 very close over the back of the pelvis, along the midrlle line. 



Tlie Ischium (Or. Icrxinv, ixcliion, the haunch-bone; ph ischia ; adj. ischiadic, ischialic, 

 better ischiac: figs. .56, 60, 61, Is) lies enth-ely post-acrtabular, or behind the socket which it 

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

 generally a thin, ]ilate-like bone. Among Cretaceous birds and existing Haiitce it only unites 

 with the ilium at and just behind the acetabnlnm, whence a deep ilio-iscliiac fissure between 

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

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

 bones behind it. Tliis vacuity, whether a notch or a hole, corresponds to the " sacro-sciatio 

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

 Rhra. 



