606 



CHOIWA TA. 



later it extends forward and back, uniting with at least nine ver- 

 tebrae and sometimes with as many as twenty-three; while the iliac 

 bones of the two sides meet dorsal to the vertebral column. This 

 extensive union of pelvis and axial skeleton is understood when 

 we recall that in walking or at rest the vertebral column is not 

 vertical as in man, but is inclined. Ischium and pubis are peculiar 

 in that they extend backwards, parallel to each other, from the 

 acetabulum, and that only exceptionally (ostrich) are the bones 

 of the two sides united by a symphysis. 



In the hind limbs occur conditions similar to those which will 



PIG. 636.^!, leg of Buteo vulgarte. a, femur; 7>, tibio-tarsus; b', remains of fibula; c, 

 tarso-metatarsus ; c', same, front view; d l -ti a , toes. J3, lower leg of bird embryo; 

 C, of lizard. /, femur; t, tibia; jj, fibula ; x, tarsales of first row (talus); ti, tar- 

 sales of second row; between these intertarsal joint; I-F, digits. (From 

 Gegenbaur.) 



be repeated in the ungulates. The weight of the body makes it 

 necessary that the simplification found in the wing should be re- 

 peated in the lower leg and foot, and that the numerous bones 

 usually occurring in these regions be replaced by one which shall 

 support the pressure (fig. 636). Therefore the fibula, well de- 

 veloped in the embryo (B), becomes reduced to an inconspicuous 

 rudiment; the metatarsals, distinct in the embryo (B), fuse to a 



