334 THE CHICK. 



The further changes in the maims are effected very slowly. 

 The three metacarpals begin to ossify about the tenth or twelfth 

 day, but remain distinct from one another until about a month 

 after hatching, when they begin slowly to unite together ; the 

 fusion of the metacarpals with the distal row of carpals does not 

 occur until some time later. 



5. The Pelvic Girdle. 



The pelvic girdle, about the sixth day, consists of a somewhat 

 squarish plate on either side of the body, the central part of 

 which is at first directly continuous with the femur. The dorsal 

 border of the plate corresponds with the iliac region, which at 

 this stage does not extend over more than about three somites, 

 differing in this respect very markedly from its condition in the 

 adult. From the ventral and anterior border of the plate two 

 processes, prepubic and pubic, project downwards and forwards ; 

 and from the ventral and posterior border a broad ischiatic pro- 

 cess projects downwards and inwards. 



During the seventh day, the femur becomes separated off 

 from the hip girdle ; the ilium extends rapidly backwards along 

 the vertebral column, and more slowly forwards ; the ischium 

 grows backwards ; and the pubis also begins to grow backwards as 

 a slender bar, lying parallel to the ventral border of the ischium, 

 and a little way below this. The prepubic process is relatively 

 much less conspicuous than in the earlier stages. 



During the later stages of development these changes 

 become more and more marked, and the pelvis gradually acquires 

 its adult shape. The ilium elongates, both anteriorly and 

 posteriorly, becoming ultimately attached to no less than fifteen 

 vertebrae. The ischium also lengthens greatly : its hinder end 

 becomes expanded, and, shortly before the time of hatching, fuses 

 with the posterior end of the ilium, to complete the boundary of 

 the ilio-sciatic foramen. The pubes elongates still more than the 

 ischium, and forms a long slender rod, lying parallel to the ven- 

 tral edge of the ischium and projecting backwards some distance 

 beyond this. The prepubic process, which, both in its cartilagi- 

 nous condition and when ossified, appears to belong to the ilium 

 rather than to the pubes, forms in the adult a small blunt 

 process, projecting from the anterior and ventral border of the 

 acetabulum . 



