. Chordate morphology. Morphology (Animals); Chordata. fused or quite fused in the region of the acetabulum (Figure 6-52). There is a large obturator fenestra, but the ends of the ischium and pubis do not join to close this gap. The pubis is pierced near the acetabulum by an obturator fora- men. The ilium is blade-like, nearly vertical in Sphenodon, sloping down and forward in Tupmamhis. In the primitive reptile or amphibian, the pubis and ischium were broad plates, jointed to one another across the ventral midline; the ilium was a dorsally directed plate of variable shape. The pubis was pierc
. Chordate morphology. Morphology (Animals); Chordata. fused or quite fused in the region of the acetabulum (Figure 6-52). There is a large obturator fenestra, but the ends of the ischium and pubis do not join to close this gap. The pubis is pierced near the acetabulum by an obturator fora- men. The ilium is blade-like, nearly vertical in Sphenodon, sloping down and forward in Tupmamhis. In the primitive reptile or amphibian, the pubis and ischium were broad plates, jointed to one another across the ventral midline; the ilium was a dorsally directed plate of variable shape. The pubis was pierced by an obturator foramen. In the pelycosaur line (Ophiacodon and Dimetrodon), the obturator fenestra lies near the acetabulum, the bones meet- ing ventromedial to this fenestra. In the bulk of the reptiles, the obturator fenestra appears to have formed by a gradual separation of pubis and ischium, first near the midline, then with progressive increase in size until the fenestra ap- proached the acetabulum. The medioventral ends of the pubis and ischium may now secondarily approach each other. Since these types of obturator fenestrae appeared late in time, they serve to mark the two lines of reptiles. Extremes of the reptile type are observed in the crocodil- ian and in the bird. The pelvis of the bird has an antero- posteriorly drawn-out ilium with the pubis and ischium di- rected posteroventrally. The obturator fenestra is a long, thin fissure between these latter bones; the anterodorsal end of the fenestra serves as the obturator foramen. In the primi- tive bird the ischium and ilium are not connected poste- riorly, but in more advanced types this has been achieved. The pubis of the alligator is not perforated by an obtura- tor foramen, and it resembles the marsupial bone of the monotreme or marsupial, perhaps having much the same function as that bone. It does not participate in the forma- tion of the acetabulum, whereas that of the bird does. The pelvic limb parallels the
Size: 1780px × 1404px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookcollectionameri, bookcollectionbiodiversity
