80 



AVES. 



merit the hand becomes more strongly bent, or clrawn much more 

 toward the fore-arm. A peculiar arrangement of ligaments gives to 

 the arm the necessary degree of security during these complicated 

 movements. 



The Pelvis of Birds is completely closed posteriorly through the 

 union into one of the mostly elongated iliac bones with the lumbo- 

 sacral bone, but open in front, through the very general want of 

 union of the pubic bones. The iliac bones are also frequently an- 

 chylosed to the last ribs and the dorsal vertebrae. The ischium is a 

 small perpendicular plate of bone extending in the direction down- 

 ward, arid united to the iliac bones, so that the ischiatic notch is 

 converted into a large foramen situated behind the acetabulum. 

 The pubic bones are very thin, narrow, and rib-like, run parallel 

 with the lower border of the ischia, and are usually united with 

 them over a greater or lesser interval by a narrow ligament, so that 

 between the two, as in most Passeres and Palmipedes, an often 

 small but occasionally double obturator foramen is left. Frequent 

 ly, as in the Birds of Prey, this pubo-ischiadic symphysis is ossified, 

 so that both bones are united by a broad bridge ; in other birds, on 

 the contrary, as the Stork and Ibis, the two bones are not immedi- 

 ately in contact, but separated by a tendinous membrane. A part 

 of the pubis however extends beyond this symphysis ; the extremi- 

 ties of the pubis usually diverge strongly, as in many Grallae and 

 Palmipedes, but they are often expanded and converge considerably, 

 as in the Diurnal birds of Prey, the Swan, and the Diving birds. 

 A true pubic symphysis occurs however in the Ostrich, in which bird 

 alone the pelvis is therefore closed in front. The acetabulum for 

 articulation with the head of the thigh-bone, is always completely 

 perforated, the bottom of its cavity internally being merely closed 

 by ligament. Lesser peculiarities are exhibited in the conformation 

 of the pelvis by the different orders. In the Penguin however a 

 singular anomaly occurs, namely, that the hip-bones are not anchy- 

 losed to the vertebral column, but are rendered to a certain degree 

 moveable by ligamentous union ; a condition of parts which must 

 tend to increase the waddling unsteady gait of this bird upon its 

 hinder extremities, placed, as they are, so far back beneath the body. 



The Femur is constantly smaller than the bones below it which 

 constitute the leg, and is easily distinguished from that of the 

 Mammalia by a groove upon the tuberosity of its external condyle, 

 which is converted into a pulley for receiving the articulating head 

 of the fibula. Upon its head there is a groove for the insertion of 



